Calibration of layer thickness and ink volume in fabrication of encapsulation layer for light emitting device

ABSTRACT

An ink jet process is used to deposit a material layer to a desired thickness. Layout data is converted to per-cell grayscale values, each representing ink volume to be locally delivered. The grayscale values are used to generate a halftone pattern to deliver variable ink volume (and thickness) to the substrate. The halftoning provides for a relatively continuous layer (e.g., without unintended gaps or holes) while providing for variable volume and, thus, contributes to variable ink/material buildup to achieve desired thickness. The ink is jetted as liquid or aerosol that suspends material used to form the material layer, for example, an organic material used to form an encapsulation layer for a flat panel device. The deposited layer is then cured or otherwise finished to complete the process.

This application is a continuation of U.S. Utility application Ser. No.15/279,261, filed on behalf of first-named inventor Eliyahu Vronsky onSep. 28, 2016 for “Techniques For Edge Management Of Printed Layers In AFlat Panel Display,” which in turn is a continuation of U.S. Utilityapplication Ser. No. 14/627,186, filed on behalf of first-named inventorEliyahu Vronsky on Feb. 20, 2015 for “Ink-Based Layer Fabrication UsingHalftoning To Control Thickness” (issued on Nov. 15, 2016 as U.S. Pat.No. 9,496,519), which in turn is a continuation of U.S. Utilityapplication Ser. No. 14/458,005, filed on behalf of first-named inventorEliyahu Vronsky on Aug. 12, 2014 for “Ink-Based Layer Fabrication UsingHalftoning To Control Thickness” (issued on Mar. 31, 2015 as U.S. Pat.No. 8,995,022). U.S. Utility application Ser. No. 14/458,005 in turnclaims priority to each of U.S. Provisional Application No. 62/019,076,filed on behalf of first-named inventor Eliyahu Vronsky on Jun. 30, 2014for “Ink-Based Layer Fabrication Using Halftoning to Control Thickness,”U.S. Provisional Application No. 62/005,044, filed on behalf offirst-named inventor Eliyahu Vronsky on May 30, 2014 for “Ink-BasedLayer Fabrication Using Halftoning to Control Thickness,” U.S.Provisional Application No. 61/977,939, filed on behalf of first-namedinventor Eliyahu Vronsky on Apr. 10, 2014 for “Ink-Based LayerFabrication Using Halftoning to Control Thickness,” and U.S. ProvisionalApplication No. 61/915,149, filed on behalf of first-named inventorEliyahu Vronsky on Dec. 12, 2013 for “Ink-Based Layer Fabrication UsingHalftone Variation.” Priority is claimed to each of the aforementionedapplications and each of the aforementioned applications is herebyincorporated by reference.

BACKGROUND

Various chemical and physical deposition processes can be used todeposit materials over a substrate. Some deposition processes rely onpatterned deposition, where a mask or other mechanism is used to createnanoscale features within precise tolerances, for example, matchingdimensions of electronic nanoscale structures such as transistor pathwidths, while other deposition processes provide relatively featureless,large scale deposition, such as blanket based coatings or depositionsthat span tens of microns of distance or more.

There exists a class of fabrication applications for which existingprocesses are suboptimal. More specifically, for applications where onedesires to form a layer over a large region of the substrate relative tonanoscale features, particularly for organic materials deposition, itcan be difficult to control uniformity of the deposited layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing an embodiment of disclosed techniques, inwhich thickness data for a desired layer is converted to a halftonepattern useful for fabricating the desired layer.

FIG. 1B is an illustrative diagram of a process in which layout datadescribing a desired layer is generated or received, converted into ahalftone pattern, and used to deposit ink that will become a desiredlayer.

FIG. 1C is a block diagram of a detailed embodiment, where thicknessdata is used to obtain grayscale values for respective “print cells,”and where the grayscale values are then used to generate a halftonepattern.

FIG. 2A provides an illustrative view showing a series of optionaltiers, products or services that can each independently embodytechniques introduced herein.

FIG. 2B provides a plan view of a fabrication mechanism that can be usedto fabricate a component, for example, a flat panel device in presenceof a controlled atmospheric environment.

FIG. 2C is a plan view showing layout of a printer within thefabrication mechanism of FIG. 2B; more specifically, FIG. 2C shows how aprint head 259 is moved relative to a substrate 253.

FIG. 2D is a block diagram of various subsystems associated within aprinting module of FIG. 2A.

FIG. 3A shows a way of defining a waveform used to create an individualink droplet according to discrete waveform segments.

FIG. 3B shows an embodiment where droplets having different parameterscan be created based on different nozzle firing waveforms.

FIG. 3C shows circuitry associated with generating and applying adesired waveform at a programmed time (or position) to a nozzle of aprint head; this circuitry provides one possible implementation of eachof circuits 343/351, 344/352 and 345/353 from FIG. 3B, for example.

FIG. 4A provides a flow chart used to describe conversion of datarepresenting thickness of a desired layer to a halftone image.

FIG. 4B provides another flow chart used to describe conversion of datarepresenting thickness of a desired layer to a halftone image.

FIG. 4C is a flow diagram associated with halftoning calibration.

FIG. 4D is a flow diagram associated with droplet measurement andqualification.

FIG. 5A shows one halftone pattern representing a specific ink volumefor a print cell.

FIG. 5B shows another halftone pattern representing a specific inkvolume; more particularly, FIG. 5B is used, relative to the halftonepattern of FIG. 5A, to discuss frequency modulated (“FM”) halftoning.

FIG. 5C shows another halftone pattern representing a specific inkvolume; more particularly, FIG. 5C is used, relative to the halftonepattern of FIG. 5A, to discuss amplitude modulated (“AM”) halftoning.

FIG. 5D shows the optional use of complementary (or “stitched”) halftonepatterns for adjacent tiles.

FIG. 5E shows a halftone pattern where droplet size (or shape) has beenvaried to compensate for a misfiring adjacent nozzle.

FIG. 5F shows a halftone pattern where droplets have been “borrowed” byone nozzle to compensate for a misfiring adjacent nozzle.

FIG. 6A is a chart showing grayscale values assigned to different printcells in dependence on thickness data.

FIG. 6B is another chart showing grayscale values assigned to differentprint cells in dependent on thickness data, but with grayscalecorrections added in to smooth or correct error in resultant filmthickness.

FIG. 7A provides a graph used to explain how different halftone dropletdensities are associated with different grayscale values to producedesired layer thicknesses.

FIG. 7B schematically depicts one or more border regions of a substrate,and how halftoning and/or grayscale selection can be varied in theborder regions to mitigate edge build-up.

FIG. 7C shows one possible scheme for halftoning near a border region,more particularly, for use at a corner of a deposited layer.

FIG. 7D shows edge enhancement of a print cell to provide a consistentlayer edge.

FIG. 7E shows the use of both border adjacent halftone variation, toavoid edge buildup, and “fencing” to improve edge linearity.

FIG. 8A shows a substrate 801 that will be arrayed into multiple flatpanels, for example, multiple organic light emitting diode (“OLED”)display panels, solar panels, or other types of panels.

FIG. 8B shows the substrate of FIG. 8A after active elements andelectrodes have been added to the substrate of FIG. 8A.

FIG. 8C provides a cross-sectional view of the substrate of FIG. 8B,taken along lines C-C from FIG. 8B.

FIG. 8D shows the substrate of FIG. 8C after encapsulation (840) hasbeen added; FIG. 8D also provides a close up showing that theencapsulation (840) can be formed of many individual layers, such asalternating organic and inorganic layers.

FIG. 8E shows the substrate of FIG. 8D in a plan view (i.e., from thesame perspective as FIG. 8B).

FIG. 9 is a block diagram of one process for depositing an organicencapsulation layer.

The subject matter defined by the enumerated claims may be betterunderstood by referring to the following detailed description, whichshould be read in conjunction with the accompanying drawings. Thisdescription of one or more particular embodiments, set out below toenable one to build and use various implementations of the technologyset forth by the claims, is not intended to limit the enumerated claims,but to exemplify their application. Without limiting the foregoing, thisdisclosure provides several different examples of techniques forfabricating a materials layer using halftoning to control ink dropletdensity in a manner that will produce a desired thickness of thedeposited layer. These techniques can be embodied as software forperforming these techniques, in the form of a computer, printer or otherdevice running such software, in the form of control data (e.g., a printimage) for forming the materials layer, as a deposition mechanism, or inthe form of an electronic or other device (e.g., a flat panel device orother consumer end product) fabricated using these techniques. Whilespecific examples are presented, the principles described herein mayalso be applied to other methods, devices and systems as well.

DETAILED DESCRIPTION

This disclosure provides techniques for fabricating a layer on asubstrate using a printing process. More specifically, data representinglayer thickness is received and translated using halftoning to producean ink jet droplet pattern. The ink is a viscous material such thatdroplets spread to a limited extent and, thus, the more dropletsdeposited per unit area (i.e., per cell location) the greater thethickness of the resultant layer.

In some embodiments, layer thickness is first converted to a grayscalevalue for each of a number of “print cells,” with each print cellrepresenting a unit area of substrate that has a common thickness value.For example, each print cell can be the smallest unit area representableby a dedicated thickness value. The gray scale values are then used togenerate halftoning in a manner that will result in ink droplet densitywhich produces the desired thickness. Note that this intermediate stepof using print cells to locally represent thickness is optional.

In other embodiments, these processes are used to produce anencapsulation layer that will provide a barrier to prevent exposure of asubstrate to materials such as oxygen and water. Halftoning can beselected to yield a continuous layer (i.e., after drop spreading, thedeposition area in question is completely covered with ink, with noholes or voids) but with a variable ink volume (and associated,resultant variable thickness). Note that the halftoning can be expressedor applied in a number of manners, using single print head passes,multiple print head passes, and/or any other techniques that usemultiple droplets at respective droplet locations to control theaggregate volume of a deposited ink.

A number of further, optional implementation variations can be appliedto the techniques introduced above. First, calibration processes can beused (given variation in ink viscosity or other factors for example) tomap different layer thicknesses to different grayscale values. Toprovide an introductory example, if it is desired to deposit a layer of5.0 microns uniform thickness, this thickness data can first beconverted to a grayscale value (e.g., a number within the range of 0-255such as the number “103”) with the number “103” being pre-associatedwith a given halftone droplet density that, given the ink in questionand other process particulars, will produce a 5.0 micron-thick layerfollowing printing and any associated cure process). Generally speaking,halftoning is performed as a single operation for an entire substratearea in question, but this process can also optionally be separatelyperformed for respective “tiles” of a deposited layer, with halftoneselection performed for each tile in a manner such that tiles havecomplementary droplet patterns so as to permit “seamless” stitchingtogether of adjacent droplet patterns (i.e., to avoid Mura effect).Second, any one of a number of error correction processes can be appliedto help ensure uniformity of a deposited layer. These variations will befurther discussed below.

Thus, in one embodiment, desired layer thickness is first specified asan input. This thickness can optionally be first converted to agrayscale value, e.g., a value such as a percentage, e.g., “50%” oranother relative ink volume measure. For example, in one contemplatedimplementation, a correlation between volume of applied ink and desiredthickness will have been empirically determined in advance, and so,selecting such a value results in effective selection of a volume of inkthat will build the desired thickness; it is also possible to useperiodic calibration or dynamic measurement with feedback to arrive at alinkage between any desired thickness and the volume of ink that willultimately produce the desired thickness. The conversion step can beperformed for each of multiple print cell locations that will form partof the deposition area, optionally to develop a grayscale imagerepresenting an aggregation of the grayscale values of the respectiveprint cells (see e.g., the discussion of FIGS. 6A and 6B, below). Basedon these values, a halftone pattern is then selected or generated wherethe halftone pattern will result in the desired layer thicknessresulting after any cure process for the deposited material. Note thatthe print cells can have any size relative to a halftone grid that ispertinent to the particular implementation. For example, in oneembodiment, the print cells are small, having one or more print cellsper halftone grid point (i.e., per possible halftone droplet). Inanother embodiment, print cells are relatively large, i.e., with manyhalftone grid points per print cell. A halftoning algorithm can beinvoked to generate a droplet pattern that will produce the desiredthickness, e.g., with droplets having relatively large dot gain, butwith relatively sparse droplet ejections across halftone grid points;thus, even though every print cell might have a grayscale value of “103”(e.g., corresponding to a hypothetical desired layer thickness of 5.0microns), not every associated halftone grid point will necessarilyfeature a droplet ejection.

Two specific non-limiting applications discussed below respectively usethese techniques to regulate thickness of an encapsulation layer fororganic light emitting diode devices (“OLEDs”) and solar panels. Inthese applications, it is typically desired that an encapsulation layershould be impermeable to oxygen and water. Thus, the techniques justdiscussed can optionally be used to fabricate the encapsulation layer soas to provide that impermeability. Note that the general techniques canalso be applied to deposition of other types of materials, organic andinorganic, and to the fabrication of other types of layers (e.g., otherthan encapsulation layers) and other types of devices. The disclosedtechniques are especially useful for the deposition of materials whichare to be deposited by liquid or other fluidic deposition processes(e.g., in the form of fluidic ink, whether liquid or vapor); forexample, these techniques may readily be applied to depositions oforganic materials suspended in a liquid medium. Note also that a typicaldeposition process deposits only one ink to build each layer (e.g., thelayer is effectively monochromatic); this however is not required forall embodiments, and it is also possible to use multiple inks (forexample, the mentioned processes can be used to deposit different lightgenerating materials in three respective, fluidically isolated “pixelwells” associated with generation of red, green and blue component lightfor each image pixel of an OLED display panel, such as used in sometelevisions). Also note that the term “layer” is used in multiplesenses, e.g., an encapsulation layer typically includes one or moreconstituent film layers, with the individual film layers as well as theaggregate each being an encapsulation “layer.”

As used herein, the term “halftoning” refers to the process ofgenerating or selecting a pattern of multiple droplets to apply avariable amount of ink responsive to desired layer thickness for a unitarea (e.g., per print cell, per substrate or per unit of substratearea), with a “halftone pattern” being the pattern created by thatprocess. In a typical embodiment discussed herein, halftoning isperformed based on one or more grayscale values to produce a halftonepattern that locally represents layer thickness using a droplet patternof variable droplet density (i.e., dependent on local grayscale value ora locally-weighted function of grayscale values), with each dropletposition in a halftone grid being expressed as a Boolean value (i.e., 1bit); each Boolean value (bit) denotes whether or not a nozzle is toeject a droplet at that position. A “halftone print image” represents ahalftone pattern representing the entire print area. A “grayscale value”refers not to color (e.g., white versus gray versus black), but to avalue that represents a variable layer thickness measure for a unit areaof substrate that is to receive printing; for example, in oneembodiment, a “small” grayscale value implies that a given print cellwill receive a relatively small volume of ink (e.g., low density ofdroplets), corresponding to a relatively thin layer thickness for anarea represented by the given print cell, while a “large” grayscalevalue implies that a given print cell will receive a larger volume ofink (relatively high density of droplets) corresponding to a thickerlayer. Because layer thickness equals ink volume per unit area,grayscale value is used in many embodiments herein to specify layerthickness for a given unit area. Each grayscale value is typically amulti-bit value, e.g. 8 or 16 bits, but his need not be the case for allembodiments. A “grayscale pattern” is a pattern of any one or moregrayscale values, whereas a “grayscale print image” or “grayscale image”is a grayscale pattern representing the print area, e.g., the substrate.A grayscale print image typically features an array of values that areeach multi-bit (i.e., grayscale values) where each value representslayer thickness per a corresponding unit area; by contrast, a halftoneprint image typically features an array of single bit values that eachrepresent whether or not an individual droplet will be ejected at aspecific position. For many embodiments discussed below, particularlythose geared to producing impermeable layers or layers with uniformthickness, halftone patterns used for printing are typically chosen(given dot gain/ink spreading) to produce a continuous layer, withoutholes or voids, though with different ink volumes. Note that in suchapplications, the inks in question typically comprise a monomer, apolymer, or a solvent that suspends a material, with the ink beingdried, cured or otherwise processed after deposition so as to form thedesired layer thickness as a permanent layer.

FIGS. 1A-1C are used to introduce several embodiments of the techniquesintroduced above.

FIG. 1A illustrates a first embodiment 101. Data is receivedrepresenting a layer that is to be deposited over a substrate, asindicated by numeral 103. The substrate can be any underlying materialor support surface, for example, glass or another surface, with orwithout previously deposited structures (e.g., such as electrodes,pathways or other layers or elements); it is not required that theunderlying substrate be flat. Note that the received data will typicallybe presented as part of an electronic file representing a circuit orstructure to be fabricated and, for the layer to be deposited, typicallyincludes data defining x-y plane boundaries of the layer and datarepresenting thickness at various points across the desired layer orwithin a structure of such a layer, for example, in a pixel well. Toprovide a non-limiting example, the underlying substrate could be anorganic device such as an organic light emitting device or organic lightemitting diode (“OLED”) display panel in an intermediate state offabrication, and the received data could indicate that the layer is tobe part of an encapsulation of an active region of the OLED display thatwill seal that region against oxygen and water. The received data insuch an encapsulation example would typically indicate where theparticular encapsulation layer starts and stops (e.g., x and y edgecoordinates) and its thickness as a height (e.g., a z-axis thickness of“5.0 microns”), with the height expressed as thicknesses for one or morevarious points. In one example, this layer data includes a thicknessvalue for each point on an x-y grid system, though this is not requiredfor all implementations (e.g., other coordinate systems could be used,and thickness for example could be expressed as a single uniform value,as a gradient, or using other means). As indicated by numeral 105, thereceived data is, using processes described herein, converted to ahalftone pattern that will be used to influence deposition of layermaterial using a printing process, e.g., an ink jet printing process, toproduce the desired layer thickness. Whether or not desired layerthickness is provided on a point-by-point basis, the thickness data isderived for each print cell that will be addressed by the printingprocess, and is then used to select a specific halftone pattern whoseresultant droplets “build” the layer in question. Note that therelationship between print cell and halftone grid (i.e., dropletdensity) is arbitrary. In one embodiment, each print cell equates to aspecific grid point, i.e., there is a one-to-one relationship. In asecond embodiment, each print cell corresponds to more than one gridpoint (i.e., an integer or non-integer number of grid points). In yet athird embodiment, each grid point corresponds to a more than one printcell (i.e., an integer or non-integer number of print cells). Perdashed-line box 106 and as mentioned already, in one embodiment, thehalftone pattern is optionally constrained to always produce a locallycontinuous film, though with variable ink volume dependent on desiredlayer thickness. The halftone patterns can be optionally determined inadvance (e.g., with one to many halftone patterns that could be used pergrayscale value or average of grayscale values), for example, so as toprovide a capability to vary pattern selection; in another embodiment,droplet density is calibrated as a function of average grayscale valueand is used “on the fly” to determine halftone patterning representing aset of grayscale values. In one embodiment, a set of grayscale values,each multi-bit, provides an input to halftone selection software, whichthen returns an output halftone pattern (e.g., with droplets positionedrelative to a halftone grid, and with the decision to fire or not fire adroplet at a given grid point expressed as a single bit). The halftonepattern can be expressed as printer instructions (e.g., a print image tocontrol a printer to print droplets at specific locations). Theseinstructions contain information that will responsively cause the inkjet printing process to deposit ink at volume per unit area that islocally varied according to the information represented by the halftonepattern, with a greater aggregate print cell ink volume for thickerlayers, and a lesser aggregate print cell ink volume for thinner layers.

Box 110, and media graphic 111, represent that, in one embodiment, thesteps just introduced can be embodied as instructions stored onnon-transitory machine-readable media, e.g., as software.“Non-transitory machine-readable media” means any tangible (i.e.,physical) storage medium, irrespective of how data on that medium isstored, including without limitation, random access memory, hard diskmemory, optical memory, a floppy disk or CD, server storage, volatilememory and other tangible mechanisms where instructions may subsequentlybe retrieved by a machine. The machine-readable media can be instandalone form (e.g., a program disk) or embodied as part of a largermechanism, for example, a laptop computer, portable device, server,network, printer, or other set of one or more devices. The instructionscan be implemented in different formats, for example, as metadata thatwhen called is effective to invoke a certain action, Java code orscripting, code written in a specific programming language (e.g., as C++code) or a processor-specific instruction set, or in some other form;the instructions can also be executed by the same processor or differentprocessors, depending on embodiment. For example, in one implementation,instructions on non-transitory machine-readable media can be executed bya single computer and, in other cases as noted, can be stored and/orexecuted on a distributed basis, e.g., using one or more servers, webclients, or application-specific devices.

The halftoning produced by the process of box 110 can be employedimmediately and/or stored for later use. To this effect, FIG. 1A showsthat halftoning can be stored as a printer control file 107 (e.g.,printer control instructions), for example, also on non-transitorymachine-readable media 113. This media can be the same media asrepresented by media graphic 111, or different media, e.g., the RAM orhard disk of a desktop computer or printer, a disk, or a flash card. Asa non-limiting example, such printer control instructions could be madeavailable as a network-stored reference design which is adapted fordownload or transmission to an electronic destination. For mostapplications, as indicated by optional process block 109, the appliedhalftoning will ultimately be used to deposit a layer using thementioned ink jet printing process. Once the layer deposition steps (andany post-deposition curing or other finishing steps) are complete, thedeposited layer in the region of deposition will have a thickness thatcorresponds to the intended layer thickness, as a function of thehalftoning.

FIG. 1B is an illustrative diagram showing a process and hardware forfabricating a layer, such as the layer just discussed with reference toFIG. 1A. The process and hardware are generally represented by numeral151 and are seen to include one or more computers 153 that are able toreceive layout data for one or more layers of material (e.g., as part ofa design file). This layout data and any associated design file aregenerated by and received from a computer 155, for example a computerused for computer-assisted design (“CAD”). The received layout data(including any design file) can be part of instructions or data storedon machine-readable media where the data or instructions can be used tofabricate the desired component, for example, a consumer electronicproduct or another product. The layout data is optionally received overa network 157, for example a local area network (“LAN”) or wide areanetwork (“WAN,” such as the Internet or a private network of a company).In some embodiments, the computer 155 is optionally itself one of theone or more computers 153, i.e., design of the layer and generation ofprinter control instructions can optionally be performed on one computeror within a single local network. The one or more computers 153 applyprocessing as introduced above, that is, to convert thickness data for alayer to at least one halftone pattern. The results of halftoning arestored in local memory 159 and are optionally transmitted to an ink jetprinting mechanism 161 via network 163. Note that the one or morecomputers 153 can also be combined with the ink jet printing mechanism,e.g., these elements can be embodied as a control terminal for afabrication mechanism that includes an ink jet printer that will formthe desired layer, e.g., as one or more scans that print the layer, eachscan as a single pass over an area of substrate, to deposit the desiredlayer thickness, e.g., following any cure or finishing procedure. Theink jetted by the ink jet printing mechanism typically includes amaterial (e.g., an organic material) jetted as a fluid, as mentioned. Asintroduced above and as further described below, in some embodiments,each print cell corresponding to the unit printable area of thesubstrate is assigned a discrete ink volume (e.g., in the form of agrayscale value). The size of a print cell is arbitrary and typicallyrepresents the minimum unit of substrate area that can or will beassigned a discrete thickness (i.e., grayscale value). Each print cellin turn is typically associated with one or more points on a grid wherethe points of the grid each represent possible, respective ink dropletpositions. The firing of each possible droplet is controlled responsiveto applied halftoning. In one embodiment, “frequency modulated”halftoning is used, meaning that the firing of droplets from respectiveprint head nozzles (or positions) is performed at a specific spatialfrequency, varied according to the desired layer thickness (e.g., seeFIG. 5A). In another embodiment, “amplitude modulated” halftoning isused, that is, where droplet firings are in spatially-separatedclusters, with the number of droplets per cluster varied according todesired thickness; thus a darker image (i.e., thicker layer) isrepresented by bigger apparent drops than a thinner layer, again in thisembodiment, with dot gain sufficient to achieve a locally continuousfilm notwithstanding grid points where droplets are not fired (e.g., seeFIG. 5C). In still other embodiments, droplet size and/or shape can bevaried (e.g., from circular or elliptical or some other shape) bychanging the electrical pattern used to fire one or more ink jetnozzles; alternatively or in addition, the halftone pattern and/orprinter instructions can instruct multiple passes of a specific scanposition by an ink jet print head. Finally, other techniques can also beused, alone or in combination with the techniques mentioned above. Theseoptional features are represented by optional process block 165.

The processing of inputted layout data results in layer thickness databeing identified for each print cell and, then, being converted to agrayscale value representing the particular print cell. For example, inone embodiment, the grayscale value is an eight-bit field having 256possible values; if layer thickness were to range between one micron andeleven microns, then a thickness measure representing six microns (i.e.,exactly intermediate thickness in the range) might be converted to thegrayscale value “128.” A halftone pattern (e.g., representing a locallycontinuous film) is then selected dependent on one or more of theassigned grayscale values, per numeral 167. Note again that therelationship between desired layer thickness and grayscale value neednot be linear. For example, if a minimum eight-bit value of, e.g., “67”was needed to achieve a continuous film for a particular embodiment,then an assigned thickness might be represented by a number in the rangeof 0, 67-255.

FIG. 1B also introduces an optional (dashed-line) process, 169, relatingto the use of error correction data (or other data) to influencehalftoning. This can be applied in a number of ways, but to provide oneintroductory example, if it is determined in practice for a particularprinting mechanism that a subset of ink nozzles are inoperative, thehalftone pattern can be optionally adjusted to provide compensation(e.g., the pattern can be varied, or AM halftoning can be appliedinstead of FM halftoning, or another scheme can be used), or the printhead can be instructed to use different nozzles (e.g., with an optionaloffset in scan path); as such error data would presumably affect eachpass of a subject-print head over the substrate, the halftoningalgorithm can optionally be updated, at least for the subject-printhead, to perform future printing or print planning using modifiedparameters. In other embodiments, drive waveforms for a particular inknozzle can be varied or tuned. For example, process variations for eachnozzle (and other factors such as nozzle life/age and ink parameterssuch as viscosity, surface tension and temperature) can influenceper-nozzle droplet volume; to mitigate this effect, the drive waveformfor the nozzle can be varied in order to adjust volume, trajectory orvelocity of an ejected droplet that contributes to an assigned ordesired halftone pattern. Similar corrections/updates can be supplieddepending on deposition machine particulars, ink qualities, and otherfactors. Note that error correction can also take other forms, forexample, varying droplet size or shape, or changing the spatialpositioning of droplets within a print cell. Applicant's copending PCTPatent Application No. PCT/US14/35193 for “Techniques for Print InkDroplet Measurement and Control to Deposit Fluids within PreciseTolerances,” filed on behalf of first named inventor Nahid Harjee onApr. 23, 2014 discloses techniques for individualized droplet volume,trajectory and velocity measurement, the validation of droplets asuseable or aberrant to a point where a nozzle should be excluded fromuse, planning of print head scan paths around such issues, and theadjustment of (and provision of alternate) nozzle drive waveforms andother compensation for use in correcting such behavior; this mentionedapplication is hereby incorporated by reference, as though set forthherein. Various techniques for error correction will be discussed belowbut, as represented by optional process 169, if applied, such techniquescan be used to adjust how an individual pattern is created, to correctfor aberration in a deposited layer. Any of the techniques or processesdescribed in the aforementioned copending PCT patent applicationPCT/US14/35193 can be applied to adjust droplet generation to promoteuniform droplet generation and/or error compensation.

FIG. 1C provides yet another flow diagram used to introduce theprocesses discussed above. A method implementing these processes isgenerally identified using numeral 181. First, layer data is received(183), for example, identifying size and shape of a desired layer andthickness of the desired layer. In one embodiment, the desired layerwill be a part of a completed flat panel display (e.g., a television orother display device) and, in another embodiment, the desired layer willbe part of a solar panel. Optionally, in some implementations, thedesired layer is an encapsulation layer that will protect activeelements of such a device against oxygen and/or water. As exemplified bydashed-line box 184, layer data can be optionally expressed in the formof a width, length and height (e.g., x microns by y microns by zmicrons, as depicted). Per box 185, the thickness data (e.g., “zmicrons” in this example) is then optionally converted to grayscalevalues, one for each one of multiple print cells, according to a mapping(186). For example, if it is determined that a layer thickness of 5.0microns (i.e., z=5.0) corresponds to a specific ink volume, achieved byfiring M droplets per some unit area, then grayscale values correlatedwith this ink droplet density (i.e., per mapping 186) are assigned toeach print cell, as depicted in an example box 187. In thishypothetical, box 187 shows a grid of values “203” which (in thisexample) are already known to provide the desired ink density needed toobtain a 5.0 micron thick layer following application of ink. Pernumeral 189, grayscale values or grid values can be optionally adjusted.For example, in one contemplated embodiment, grayscale valuesrepresenting a border (e.g., periphery of a layer to be deposited) canbe adjusted to avoid buildup at layer edges (see the discussion of FIGS.7A-7E, below). Alternatively, if deposited ink has non-uniformities thatcan be linked to specific nozzles or print cells, then grayscale valuescan be adjusted so as to mitigate such non-uniformities. In anembodiment where the substrate has underlying structures (such that auniform thickness of deposited ink results in a non-uniform surfacebecause of underling active elements), then the gray scale values can beadjusted so as to level out the post-deposition surface of the newlayer. Such adjustment can be applied before or after conversion ofgrayscale values to a halftone pattern, per process 191 (or otherwiseoptionally factored into the halftoning process). The halftoning processresults in a bitmap where each grid intersection point is associatedwith a possible droplet, and where an individual grid value (e.g.,single bit value) at a grid intersection point indicates whether adroplet is to be fired at the corresponding grid intersection point, asexemplified in example box 192. The result of this process is also a setof printer control instructions, amendable for use in printing thedesired layer, for storage for later download, transfer, use ormanipulation, or for prospectively controlling a printer. The ultimateprinting operation is designated by the numeral 193 in FIG. 1C.

With the principal parts of several embodiments thus introduced, thisdescription will now provide additional detail relating to certainfabrication techniques. FIGS. 2A-D will first be used to explainparticulars of one possible deposition environment, e.g., an industrialfabrication machine that uses ink jet printing to deposit material thatwill directly form one or more permanent layers of a flat panel device.FIGS. 3A-6B will then be used to explain how halftoning can be used tocontrol to layer thickness. FIGS. 7A-7E will be used to discuss edgebuildup and boundary control. FIGS. 8A-8E will be used to narrate ahypothetical fabrication process. Finally, FIG. 9 will be used todiscuss some fabrication options in manufacturing an OLED displaydevice. These FIGS. and associated text should be understood to provideexamples only, and other analogous techniques and implementations willno doubt occur to those skilled in the art. Using the describedtechniques and devices, a printing process and more specifically an inkjet printing process can be used to deposit nearly any desired layerusing a fluidic ink, with uniform control over layer thickness providedby use of and adjustment of a halftone pattern. The described techniquesare especially useful for “blanket” depositions, that is, where featuresize of a deposited layer is large relative to any underlying nanoscalestructures, but the techniques described above are not so limited.

FIG. 2A represents a number of different implementation tiers,collectively designated by reference numeral 201; each one of thesetiers represents a possible discrete implementation of the techniquesintroduced herein. First, halftoning techniques as introduced in thisdisclosure can take the form of instructions stored on non-transitorymachine-readable media, as represented by graphic 203 (e.g., executableinstructions or software for controlling a computer or a printer).Second, per computer icon 205, these techniques can also optionally beimplemented as part of a computer or network, for example, within acompany that designs or manufactures components for sale or use in otherproducts. Third, as exemplified using a storage media graphic 207, thetechniques introduced earlier can take the form of a stored printercontrol instructions, e.g., as a halftone print image that, when actedupon, will cause a printer to fabricate one or more layers of acomponent dependent on the use of one or more halftone patternsrepresenting different ink volumes, per the discussion above. Note thatprinter instructions can be directly transmitted to a printer, forexample, over a LAN; in this context, the storage media graphic canrepresent (without limitation) RAM inside or accessible to a computer orprinter, or a portable media such as a flash drive. Fourth, asrepresented by a fabrication device icon 209, the techniques introducedabove can be implemented as part of a fabrication apparatus or machine,or in the form of a printer within such an apparatus or machine. It isnoted that the particular depiction of the fabrication device 209represents one exemplary printer device that will be discussed inconnection with FIG. 2B, below. The techniques introduced above can alsobe embodied as an assembly of manufactured components; in FIG. 2A forexample, several such components are depicted in the form of an array211 of semi-finished flat panel devices, that will be separated and soldfor incorporation into end consumer products. The depicted devices mayhave, for example, one or more encapsulation layers or other layersfabricated in dependence on the methods introduced above. The techniquesintroduced above can also be embodied in the form of end-consumerproducts as referenced, e.g., in the form of display screens forportable digital devices 213 (e.g., such as electronic pads or smartphones), as television display screens 215 (e.g., OLED TVs), solarpanels 217, or other types of devices.

FIG. 2B shows one contemplated multi-chambered fabrication apparatus 221that can be used to apply techniques disclosed herein. Generallyspeaking, the depicted apparatus 221 includes several general modules orsubsystems including a transfer module 223, a printing module 225 and aprocessing module 227. Each module maintains a controlled environment,such that printing for example can be performed by the printing module225 in a first controlled atmosphere and other processing, for example,another deposition process such an inorganic encapsulation layerdeposition or a curing process (e.g., for printed materials), can beperformed in a second controlled atmosphere. The apparatus 221 uses oneor more mechanical handlers to move a substrate between modules withoutexposing the substrate to an uncontrolled atmosphere. Within any givenmodule, it is possible to use other substrate handling systems and/orspecific devices and control systems adapted to the processing to beperformed for that module.

Various embodiments of the transfer module 223 can include an inputloadlock 229 (i.e., a chamber that provides buffering between differentenvironments while maintaining a controlled atmosphere), a transferchamber 231 (also having a handler for transporting a substrate), and anatmospheric buffer chamber 233. Within the printing module 225, it ispossible to use other substrate handling mechanisms such as a flotationtable for stable support of a substrate during a printing process.Additionally, a xyz-motion system, such as a split axis or gantry motionsystem, can be used for precise positioning of at least one print headrelative to the substrate, as well as providing a y-axis conveyancesystem for the transport of the substrate through the printing module225. It is also possible within the printing chamber to use multipleinks for printing, e.g., using respective print head assemblies suchthat, for example, two different types of deposition processes can beperformed within the printing module in a controlled atmosphere. Theprinting module 225 can comprise a gas enclosure 235 housing an inkjetprinting system, with means for introducing an inert atmosphere (e.g.,nitrogen) and otherwise controlling the atmosphere for environmentalregulation (e.g., temperature and pressure), gas constituency andparticulate presence.

Various embodiments of a processing module 227 can include, for example,a transfer chamber 236; this transfer chamber also has a including ahandler for transporting a substrate. In addition, the processing modulecan also include an output loadlock 237, a nitrogen stack buffer 239,and a curing chamber 241. In some applications, the curing chamber canbe used to cure a monomer film into a uniform polymer film, for example,using a heat or UV radiation cure process.

In one application, the apparatus 221 is adapted for bulk production ofliquid crystal display screens or OLED display screens, for example, thefabrication of an array of eight screens at once on a single largesubstrate. These screens can be used for televisions and as displayscreens for other forms of electronic devices. In a second application,the apparatus can be used for bulk production of solar panels in muchthe same manner.

Applied to the encapsulation example discussed above, and adapted to usethe halftone-based printing techniques described above, the printingmodule 225 can advantageously be used in such applications to depositorganic encapsulation layers that help protect the sensitive elements ofsuch devices. For example, the depicted apparatus 221 can be loaded witha substrate and can be controlled to move the substrate back and forthbetween the various chambers in a manner uninterrupted by exposure to anuncontrolled atmosphere during the encapsulation process. The substratecan be loaded via the input loadlock 229. A handler positioned in thetransfer module 223 can move the substrate from the input loadlock 229to the printing module 225 and, following completion of a printingprocess, can move the substrate to the processing module 227 for cure.By repeated deposition of subsequent layers, each of controlledthickness, aggregate encapsulation can be built up to suit any desiredapplication. Note once again that the techniques described above are notlimited to encapsulation processes, and also that many different typesof tools can be used. For example, the configuration of the apparatus221 can be varied to place the various modules 223, 225 and 227 indifferent juxtaposition; also, additional, fewer or different modulescan also be used.

While FIG. 2B provides one example of a set of linked chambers orfabrication components, clearly many other possibilities exist. Thehalftoning techniques introduced above can be used with the devicedepicted in FIG. 2B, or indeed, to control a fabrication processperformed by any other type of deposition equipment.

FIG. 2C provides a plan view of the substrate and printer as they mightappear during the deposition process. The print chamber is generallydesignated by reference numeral 251, the substrate to be printed upon isgenerally designated by numeral 253, and a support table used totransport the substrate is generally designated by numeral 255.Generally speaking, any x-y coordinate of the substrate is reached by acombination of movements, including x- and y-dimensional movement of thesubstrate by the support table (e.g., using flotation support, asdenoted by numeral 257) and using “slow axis” x-dimensional movement ofone or more print heads 259 along a traveler 261, as generallyrepresented by arrows 263. As mentioned, the flotation table andsubstrate handling infrastructure are used to move the substrate andadvantageously provide deskew control along one or more “fast axes,” asnecessary. The print head is seen to have plural nozzles 265, each ofwhich is separately controlled by a firing pattern derived from ahalftone print image (e.g., to effectuate printing of columns of printcells as the print head is moved from left-to-right and vice-versa alongthe “slow axis”). Note that while only 5 nozzles are depicted in FIG. 2Cthat any number of nozzles can be used; for example, in a typicalindustrial printing implementation, there can be multiple print headswith thousands of nozzles present. With relative motion between the oneor more print heads and the substrate provided in the direct of the fastaxis (i.e., the y-axis), printing describes a swath that followsindividual rows of print cells. The print head can also advantageouslybe adjusted to vary effective nozzle spacing (e.g., by rotating of theone or more print heads, per numeral 267). Note that multiple such printheads can be used together, oriented with x-dimension, y-dimension,and/or z-dimensional offset relative to one another as desired (see axislegend 269 in FIG. 2C). The printing operation continues until theentire target region (and any border region) has been printed with ink,as desired. Following deposition of the necessary amount of ink, thesubstrate is finished, either by evaporating solvent to dry ink (e.g.,using a thermal process), or by use of a cure process, such as a UV cureprocess.

FIG. 2D provides a block diagram showing various subsystems of oneapparatus (271) that can be used to fabricate devices having one or morelayers as specified herein. Coordination over the various subsystems isprovided by a processor 273, acting under instructions provided bysoftware (not shown in FIG. 2D). During a fabrication process, theprocessor feeds data to a print head 275 to cause the print head toeject various volume of ink depending on firing instructions provided bya halftone print image. The print head 275 typically has multiple inkjet nozzles, arranged in a row or array, and associated reservoirs thatpermit jetting of ink responsive to activation of piezoelectric or othertransducers; such transducers cause a respective nozzle to eject acontrolled amount of ink in an amount governed by an electronic firingwaveform signal applied to the corresponding piezoelectric transducer.Other firing mechanisms can also be used. The print head applies the inkto a substrate 277 at various x-y positions corresponding to the gridcoordinates within various print cells, as represented by the halftoneprint image. Variation in position is effected both by a print headmotion system 279 and substrate handling system 281 (e.g., that causethe printing to describe one or more swaths across the substrate). Inone embodiment, the print head motion system 279 moves the print headback-and-forth along a traveler, while the substrate handling systemprovides stable substrate support and both “x” and “y” dimensiontransport (and rotation) of the substrate, e.g., for alignment anddeskew; during printing, the substrate handling system providesrelatively fast transport in one dimension (e.g., the “y” dimensionrelative to FIG. 2C), while the print head motion system 279 providesrelatively slow transport in another dimension (e.g., the “x” dimensionrelative to FIG. 2C), e.g., for print head offset. In anotherembodiment, multiple print heads can be used, with primary transportbeing handled by the substrate handling system 281. An image capturedevice 283 can be used to locate any fiducials and assist with alignmentand/or error detection.

The apparatus also comprises an ink delivery system 285 and a print headmaintenance system 287 to assist with the printing operation. The printhead can be periodically calibrated or subjected to a maintenanceprocess; to this end, during a maintenance sequence, the print headmaintenance system 287 is used to perform appropriate priming, purge ofink or gas, testing and calibration, and other operations, asappropriate to the particular process. Such a process can also includeindividual measurement of parameters such as droplet volume, velocityand trajectory, for example, as discussed in Applicant's copending PCTpatent application referenced earlier (PCT/US14/35193), and asreferenced by numerals 291 and 292.

As was introduced previously, the printing process can be performed in acontrolled environment, that is, in a manner that presents a reducedrisk of contaminants that might degrade effectiveness of a depositedlayer. To this effect, the apparatus includes a chamber controlsubsystem 289 that controls atmosphere within the chamber, as denoted byfunction block 290. Optional process variations, as mentioned, caninclude performing jetting of deposition material in presence of anambient nitrogen gas atmosphere (or another inert environment, having aspecifically selected gas and/or controlled to exclude unwantedparticulate). Finally, as denoted by numeral 293, the apparatus alsoincludes a memory subsystem that can be used to store halftone patterninformation or halftone pattern generation software, i.e., should theapparatus directly perform rendering of layout data to obtain a halftoneprint image according to the techniques introduced above, to internallygenerate printer control instructions that govern the firing of (andtiming of) each droplet. If such rendering is performed elsewhere, andthe task of the apparatus is to fabricate a device layer according to areceived printer instructions, then the halftone print image can bestored in the memory subsystem 293 for use during the printing process.As noted by numeral 294, in one optional embodiment, individual dropletparticulars can be varied (e.g., to correct for nozzle aberration)through the variation of firing waveform for any given nozzle. In oneembodiment, a set of alternate firing waveforms can be selected inadvance and made available to each nozzle, on a shared or dedicatedbasis. In another embodiment, a single waveform is decided upon inadvance (e.g., selected relative to alternatives) and is programmed forindefinite use in connection with a specific nozzle.

Structure and techniques for modifying or tuning nozzle firingparticulars are explained with reference to FIGS. 3A-3C. In oneembodiment, waveforms can be predefined as a sequence of discrete signallevels, e.g., defined by digital data, with a drive waveform beinggenerated by a digital-to-analog converter (DAC). Numeral 301 in FIG. 3Aidentifies a graph of a waveform 303 having discrete signal levels, 304,305, 306, 307, 308, 309 and 310. In one embodiment, each nozzle drivercan include circuitry that receives multiple waveforms (e.g., up tosixteen or another number), with each waveform being defined as a seriesof signal levels of variable voltage and duration. Each waveform can beexpressed as a sequence of up to sixteen such signal levels, eachexpressed as a multi-bit voltage and a multi-bit duration. That is tosay, in such an embodiment, pulse width can effectively be varied bydefining different durations for one or more signal levels, and drivevoltage can be waveform-shaped in a manner chosen to provide subtledroplet size, velocity or trajectory variation, e.g., with dropletvolumes gauged to provide specific volume gradations increments such asin units of 0.01 pL. Thus, with such an embodiment, waveform shapingprovides ability to tailor droplet volumes and flight parameters to beclose to ideal values. These waveform shaping techniques also facilitatea strategy for reducing or eliminating Mura; for example, in oneoptional embodiment, a single assigned nozzle drive waveform is tailoredin advance for each nozzle, such that all nozzles provide uniformdroplet volume (e.g., as near as possible to 10.00 pL). In anotherembodiment, alternative predetermined waveforms are optionally madeavailable to each nozzle, with dynamic calibration (or another process)used to select (e.g., program) “the one” of the alternativepredetermined waveforms that is to be applied in the short term. Otherpossibilities also exist.

Typically, the effects of different drive waveforms and resultantdroplet volumes are measured in advance. In one embodiment, for eachnozzle, up to sixteen different drive waveforms can be stored in anozzle-specific, dedicated, 1 k static random access memory (SRAM) forlater, elective use in providing discrete volume variations, as selectedby software. With the different drive waveforms on hand, each nozzle isthen instructed droplet-by-droplet as to which waveform to apply via theprogramming of data that effectuates the specific drive waveform.

FIG. 3B is a diagram showing circuitry that can be used to such anembodiment, generally designated by numeral 321. In particular, aprocessor 323 is used to receive data defining a particular layer ofmaterial that is to be printed. As represented by numeral 325, this datacan be a layout file or bitmap file that defines desired thickness pergrid point or positional address. A series of piezoelectric transducers327, 328 and 329 generate associated respective droplet volumes 331, 332and 333, that are each dependent on many factors, including nozzle drivewaveform, nozzle-to-nozzle and print-head-to-print-head manufacturingvariations. During a calibration operation, each one of a set ofvariables can be tested for its effects on droplet volume, includingnozzle-to-nozzle variation, to determine one or more drive waveforms forthe respective nozzle, given the particular ink that will be used; ifdesired, this calibration operation can be made dynamic, for example, torespond to changes in temperature, nozzle clogging, print head age orother parameters. This calibration is represented by a dropletmeasurement device 335, which provides measured data to the processor323 for use in managing print planning and ensuing printing. In oneembodiment, this measurement data is calculated during an operation thattakes minutes, e.g., no more than thirty minutes for thousands ofnozzles and preferably much less time (e.g., for thousands of print headnozzles and potentially, for each nozzle, dozens of possible nozzlefiring waveforms). In another embodiment, such measurement can beperformed iteratively, that is to update different subsets of nozzles atdifferent points in time. A non-imaging (e.g., interferometric)technique can optionally be used for measurement, for example, asdescribed in the aforementioned copending, commonly-assigned PCT patentapplication; this potentially results in dozens of droplet measurementsper nozzle, covering dozens to hundreds of nozzles per second. This dataand any associated statistical models (and means) can be stored inmemory 337 for use in processing the layout or bitmap data 325 when itis received. In one implementation, processor 323 is part of a computerthat is remote from the actual printer, whereas in a secondimplementation, processor 323 is either integrated with a fabricationmechanism (e.g., a system for fabricating displays) or with a printer.

To perform the firing of droplets, a set of one or more timing orsynchronization signals 339 are received for use as references, andthese are passed through a clock tree 341 for distribution to eachnozzle driver 343, 344 and 345 to generate the drive waveform for theparticular piezoelectric transducer (327, 328 and 329, respectively),i.e., with a dedicated piezoelectric transducer per nozzle (and withthousands of nozzles typically present, even though only three areillustrated in FIG. 3B). Each nozzle driver has one or more registers351, 352 and 353, respectively, which receive multi-bit programming dataand timing information from the processor 323. Each nozzle driver andits associated registers receive one or more dedicated write enablesignals (we_(n)) for purposes of programming the registers 351, 352 and353, respectively. In one embodiment, each of the registers comprises afair amount of memory, including a 1 k SRAM to store multiple,predetermined waveforms, and programmable registers to select betweenthose waveforms and otherwise control waveform generation. The data andtiming information from the processor is depicted in FIG. 3B asmulti-bit information, although this information can instead be providedvia a serial connection to each nozzle (as will be seen in FIG. 3C,discussed below).

For a given deposition, print head or ink, the processor chooses foreach nozzle a set of sixteen prearranged drive waveforms that can beelectively (i.e., “at will”) applied to generate a droplet; note thatthis number is arbitrary, e.g., in one design, four waveforms could beused, while in another, four thousand could be used. These waveforms areadvantageously selected to provide desired variation in output dropletvolume for each nozzle, e.g., to cause each nozzle to have at least onewaveform choice that produces a near-ideal droplet volume (e.g., a meandroplet volume of 10.00 pL) and to accommodate a range of deliberatevolume variation for each nozzle that can be used to produce an idealdroplet size, ejection velocity and flight trajectory. In variousembodiments, the same set of sixteen drive waveforms are used for all ofthe nozzles, though in the depicted embodiment, sixteen, possibly-uniquewaveforms are each separately defined in advance for each nozzle, eachwaveform conferring respective droplet volume (and velocity andtrajectory) characteristics.

During printing, to control deposition of each droplet, data selectingone of the predefined waveforms is then programmed into each nozzle'srespective registers 351, 352 or 353 on a nozzle-by-nozzle basis. Forexample, given a target droplet volume of 10.00 pL, nozzle driver 343can be configured through writing of data into registers 351 to set oneof sixteen waveforms corresponding to one of sixteen different dropletvolumes. The volume produced by each nozzle would have been measured bythe droplet measurement device 335, with nozzle-by-nozzle (andwaveform-by-waveform) droplet volumes and associated distributionsregistered by the processor 323 and stored in memory. The processor can,by programming the register 351, define whether or not it wants thespecific nozzle driver 343 to output a processor-selected one of thesixteen waveforms. In addition, the processor can program the registerto have a per-nozzle delay or offset to the firing of the nozzle for agiven scan line (e.g., to optionally correct for substrate skew, tocorrect for error including velocity or trajectory error, and for otherpurposes); this offset is effectuated by counters which delay firing ofthe particular nozzle by a programmable number of timing pulses for eachscan. To provide an example, if the result of droplet measurementindicates that one particular nozzle's droplet tends to have a lowerthan expected velocity, then the corresponding nozzle waveform can betriggered earlier (e.g., advanced in time, by reducing a dead timepreceding the active signal levels used for piezoelectric actuation);conversely, if the result of droplet measurement indicates that the oneparticular nozzle's droplet has a relatively high velocity, then thewaveform can be triggered later, and so forth. Other examples areclearly possible—for example, a slow droplet velocity can becounteracted in some embodiments by increasing drive strength (i.e.,signal levels and associated voltage used to drive a given nozzle'spiezoelectric actuator). In one embodiment, a sync signal distributed toall nozzles occurs at a defined interval of time (e.g., one microsecond)for purposes of synchronization and in another embodiment, the syncsignal is adjusted relative to printer motion and substrate geography,e.g., to fire every micron of incremental relative motion between printhead and substrate. The high speed clock (φ_(hs)) is run thousands oftimes faster than the sync signal, e.g., at 100 megahertz, 33 megahertz,etc.; in one embodiment, multiple different clocks or other timingsignals (e.g., strobe signals) can be used in combination. The processoralso optionally programs values defining or adjusting print grid spacing(or equivalently, timing); in one implementation, the print grid spacingis common to the entire pool of available nozzles and is equal to thehalftone grid spacing, though this need not be the case for eachimplementation. For example, in some cases, a printer grid can bedefined in a manner that adjusts timing (e.g. phase) of each nozzle'sdroplet patterns so as to compensate for substrate skew or otherfactors. Thus, in one optional embodiment, nozzle firing patterns can bevaried to effectively transform the halftone grid to match a substrategeography that is a priori unknown (e.g., with software rotating oradjusting the printer instructions as necessary for proper printing).Clearly, many design alternatives are possible. Note that the processor323 in the depicted embodiment can also dynamically reprogram theregister of each nozzle during operation, i.e., the sync pulse isapplied as a trigger to launch any programmed waveform pulse set in itsregisters; if new data is asynchronously received by the depictedcircuitry before the next sync pulse (e.g., to adjust a droplet waveformand potentially droplet timing, trajectory and/or volume), then the newdata will be applied with the next sync pulse. The processor 323 alsocontrols initiation and speed of scanning (355) in addition to settingparameters for the sync pulse generation (356). In addition, theprocessor controls optional rotation of the print head (357), for thevarious purposes described above. In this way, each nozzle canconcurrently (or simultaneously) fire using any one of sixteen differentwaveforms for each nozzle at any time (i.e., with any “next” syncpulse), and the selected firing waveform can be switched with any otherof the sixteen different waveforms dynamically, in between fires, duringa single scan.

FIG. 3C shows additional detail of circuitry (361) that can be used insuch an embodiment to generate output nozzle drive waveforms for eachnozzle; the output waveform is represented as “nzzl-drv. wvfm” in FIG.3C. More specifically, the circuitry 361 receives inputs of the syncsignal, a single-ended or differential line carrying serial data(“data”), a dedicated write enable signal (we) and the high speed clock(φ_(hs)). A register file 363 provides data for at least threeregisters, respectively conveying an initial offset, a grid definitionvalue and a drive waveform ID. The initial offset is a programmablevalue that adjusts each nozzle to align with the start of a print grid.For example, given implementation variables such as multiple printheads, multiple rows of nozzles, different print head rotations, nozzlefiring velocity and patterns and other factors, the initial offset canbe used to align each nozzle's droplet pattern with the start of theprint grid, to account for delays, skew and other factors. Offsets canbe differently applied across multiple nozzles, for example, to rotate agrid or halftone pattern relative to substrate geography, or to correctfor substrate misalignment; advantageously, these functions can beperformed by software, i.e., by instructions stored on non-transitory,machine-readable media. Similarly, offsets can also be used to correctfor aberrant velocity or other effects. The grid definition value is anumber that represents the number of sync pulses “counted” before theprogrammed waveform is triggered (e.g., representing a firingfrequency); in the case of an implementation that prints flat paneldisplays (e.g., OLED panels), the halftone grid firing points presumablyhave one or more regular spacings relative to the different print headnozzles, corresponding to a regular (constant spacing) or irregular(multiple spacing) grid. Thus, if the grid spacing value was set to two(e.g., every two microns), then each nozzle could be fired at thisinterval. The drive waveform ID represents a selection of one of thepre-stored drive waveforms for each nozzle, and can be programmed andstored in many manners, depending on embodiment. In one embodiment, thedrive waveform ID is a four bit selection value, and each nozzle has itsown, dedicated 1 k-byte SRAM to store up to sixteen predetermined nozzledrive waveforms, stored as 16×16×4B entries. Briefly, each of sixteenentries for each waveform contains four bytes representing aprogrammable signal level, with these four bytes representing a two-byteresolution voltage level and a two-byte programmable duration, used tocount a number of pulses of the high-speed clock. Each programmablewaveform can thus consist of zero to up to sixteen discrete pulses eachof programmable voltage and duration (e.g., of duration equal to 0-255pulses of a 33 megahertz clock).

Numerals 365, 366 and 367 designate one embodiment of circuitry thatshows how a specified waveform can be generated for a given nozzle. Afirst counter 365 receives the sync pulse, to initiate a countdown ofthe initial offset, triggered by start of a new line scan; the firstcounter 365 counts down in micron increments and, when zero is reached,a trigger signal is output from the first counter 365 to a secondcounter 366. This trigger signal essentially starts the firing processfor each nozzle for each scan line. The second counter 366 thenimplements a programmable grid spacing in increments of microns. Thefirst counter 365 is reset in conjunction with a new scan line, whereasthe second counter 366 is reset using the next edge of the high-speedclock following its output trigger. The second counter 366, whentriggered, activates a waveform circuit generator 367, which generatesthe selected drive waveform shape for the particular nozzle. As denotedby dashed line boxes 368-370, seen beneath the generator circuit, thislatter circuit is based on a high speed digital-to-analog converter 368,a counter 369, and a high-voltage amplifier 370, timed according to thehigh-speed clock (φ_(hs)). As the trigger from the second counter 366 isreceived, the waveform generator circuit retrieves the number pairs(signal level and duration) represented by the drive waveform ID valueand generates a given analog output voltage according to the signallevel value, with the counter 369 effective to hold DAC output for aduration according to the counter. The pertinent output voltage level isthen applied to the high-voltage amplifier 370 and is output as thenozzle-drive waveform. The next number pair is then latched out fromregisters 363 to define the next signal level value/duration, and soforth.

The depicted circuitry provides an effective means of defining anydesired waveform according to data provided by the processor 323 fromFIG. 3B. Software receives print instructions and adjusts or interactswith those instructions as necessary in order to comply with or correctfor grid geometry or a nozzle with aberrant velocity or flight angle.The durations and/or voltage levels associated with any specific signallevel (including a first, “delay” signal level of zero volts, whicheffectively defines an offset relative to sync) can be adjusted to thisend. As noted, in one embodiment, the processor decides upon a set ofwaveforms in advance (e.g., sixteen possible waveforms, per-nozzle) andit then writes definition for each of these selected waveforms into SRAMfor each nozzle's driver circuitry, with a “firing-time” decision ofprogrammable waveform then being effected by writing a four-bit drivewaveform ID into each nozzle's registers.

With optional circuitry for generating individual droplets (i.e., pernozzle droplets) thus described, this disclosure will now furtherdiscuss halftone generation techniques and associated error correctiontechniques. As should be appreciated, precise controls over per-nozzledroplet volume, for example, with a well formed understanding ofper-nozzle droplet mean volume (and expected volume distribution) and asimilar understanding for droplet flight and trajectory, and withoptional circuitry for varying per-nozzle waveforms, droplet timing,droplet volume and other particulars, permits deposition of very preciseink droplets using the techniques described above.

FIG. 4A provides a method diagram 401 for controlling layer thicknessusing halftoning. These techniques can optionally be used with thewaveform tuning techniques and circuitry described above. Morespecifically, as depicted by numeral 403, layout data 403 is firstreceived and used to define the desired grid (405). This grid will beara relationship to nozzle spacing used by the printer (407) and,accordingly, software determines this relationship and uses thisrelationship to plan halftoning and print parameters such as scan path,to develop printer control instructions. Software also receives inkvolume data (409), which for example, identifies the amount of ink perunit area needed to achieve a desired layer thickness. Note that in oneembodiment, the correlation between volume and thickness is measuredafter test layer formation (e.g., after cure or drying). In a variation,the correlation is measured on the basis of thickness of wet inkfollowing one or more print head passes. In one embodiment, softwarethen maps droplet density to grid pitch (411), for example, using theformula

${{Desired}\mspace{14mu}{Thickness}} = {h \times \left\{ \frac{{Volume}_{drop}}{{Pitch}_{{in}\text{-}{scan}} \times {Pitch}_{{cross}\text{-}{scan}}} \right\}}$as also seen within dashed-line box 412. The in-scan pitch representsthe spacing between drop opportunities in a first direction of relativemotion between the print head and substrate, the cross-scan pitchrepresents the spacing between drop opportunities in a directiongenerally perpendicular to (or otherwise independent of) this firstdirection, and the parameter h (times 100) is the grayscale value inpercentage. In one embodiment, this relationship can vary over time and,thus, can be re-measured to develop empirical data (413), for dynamicfactors such as process or temperature, for specific machine or inkparticulars, for nozzle age, or for other factors.

With desired droplet density identified, software then invokes ahalftone pattern generation subroutine (or a separate software planningprocess), as represented by numeral 415. In one embodiment, thisplanning can be performed by a remote computer while, in anotherembodiment, this process is integrated with the printer. The halftonepattern generation function plans droplet deposition patterns so as toproduce droplet patterns, with each droplet having substantially uniformvolume, according to a selection of points on a halftone grid. Inanother embodiment, droplet variation is not necessarily uniform, butrather, droplet measurements are factored into halftone patterngeneration, i.e., such that selected gridpoints for droplet firingscontemplate specific droplet volumes (or trajectories or velocities)associated with nozzles firing at those points, with the halftoninggeneration accommodating (and factoring in) nozzle-to-nozzle variation.Ideally, the pattern is defined so that the spreading of ink produces alocally continuous layer of material of homogeneous thickness. Plannedas a single process covering the area of the entire layer (to bedeposited on the substrate), and according to a single halftone gridthat spans the deposition area of interest, the ink is deposited ideallyin a manner that is seamless (416), i.e., to avoid Mura. As mentionedearlier, in one embodiment, desired layer thickness is apportioned todifferent “print cells” with a thickness or grayscale value applied toeach print cell, and with the halftone generation software receiving agrayscale image (i.e., an array of grayscale values) and developing ahalftone pattern based on this grayscale image (e.g., with local inkvolume variation controlled by individual print cell values and witherror diffusion relied upon as appropriate to achieve desiredhomogeneity). As noted, in another embodiment, halftone patterns can beseparately (independently) planned for each of plural “tiles” ofadjacent deposition areas (417) with halftone droplet patterns for eachtile planned, but with halftoning performed in a complementary manner(418), such that droplet patterns are “stitched together” on a commongrid, once again to avoid Mura. This is discussed below in connectionwith FIG. 5D. Note that seamless pattern interface (e.g., “stitching”)can be enhanced through the use of a continuous grid (420). In such anembodiment, groups of one or more print cells (e.g., “m” print cells)can be equated to groups of one or more tiles (e.g., “n” tiles) and usedto generate a halftone pattern for each tile, per process 419.

FIG. 4B provides another flow diagram 421 associated with theseprocesses. As with the earlier examples, data representing layout of adesired layer is first received, per numeral 423. This data specifiesboundaries of the layer to be deposited and provides informationsufficient to define thickness throughout the layer. This data can begenerated on the same machine or device on which the process 421 isperformed, or it can be generated by a different machine. In oneembodiment, the received data is defined according to an x-y coordinatesystem and the provided information is sufficient to compute desiredlayer thickness at any represented x-y coordinate point, for example,optionally specifying a single height or thickness to be appliedthroughout the layer, consistent with the x-micron by y-micron byz-micron example introduced earlier. Per numeral 425, this data can beconverted to a grayscale value for each print cell in a deposition areathat will receive the layer. If print cell area does not inherentlycorrespond to the x-y coordinate system matching the layout data, thenthe layout data is converted (e.g., by averaging thickness data formultiple coordinate points and/or using interpolation) to obtain agrayscale value for each print cell. This conversion can be based onpredetermined mapping information, for example, produced usingrelationships or equations such as those discussed above. Per numeral427, correction can optionally be performed at this stage upon thegrayscale values in order to ultimately produce a homogeneous layer (orfor other desired effect). To provide one example (which will bediscussed further below), if it is desired to compensate for varyingheights of microstructures that will sit underneath the desired layer,an optional technique adds offsets to select grayscale values to “boost”the layer of interest at specific locations to effectively planarize atop surface of the deposited layer; for example, a desired 5.0 micronthick encapsulation layer is desired across a deposition region, andstructures defining the underlying substrate vary by e.g., a micron inthickness, then grayscale values could be manipulated to deposit 6.0micron thick encapsulation in some areas, in an effort to produce alevel top surface of the encapsulation layer. Other techniques are alsopossible. In one embodiment, such grayscale value manipulation can alsobe used to correct for nozzle firing aberration (e.g., in the in-scandirection) to deposit more ink (for example, if a particular nozzle orset of nozzles produce insufficient ink volume) or less ink (e.g., theparticular nozzle or set of nozzles produce excess ink volume). Such anoptional process can be predicated on a calibration process and/orempirically-determined data, per function block 434. The grayscalevalues are then converted to a halftone pattern, per numeral 429, witherror diffusion across the halftone grid relied upon to help ensurelocalized layer homogeneity. Based on this halftoning process, a printimage (or other printer control instructions) is then generated, pernumeral 430.

FIG. 4B also shows use of a number of optional error correctionprocesses 433, applied to help ensure uniformity in the deposited layer.Such uniformity can be important to device quality, whether to ensuredevelopment of adequate encapsulation to produce a water/oxygen barrier,or to provide high-quality light generating or light guiding elements ofa display panel, or for other purpose or effect. As noted above, acalibration process or empirically determined (dead-reckoned) data canbe used to correct grayscale values attributable to nozzle dropletvariation or other factors, per numeral 434. Alternatively, individualnozzle drive waveforms can be planned or adjusted to correct error, asrepresented by numeral 435. In yet another embodiment, nozzles can bevalidated or qualified (439), with each nozzle either determined to meetminimum droplet generation thresholds or disqualified from use. If aspecific nozzle is disqualified, then in order to generate the desiredhalftone pattern, a different nozzle (or repeated pass of acceptablenozzles) can be used to deposit the droplet(s) that would otherwise havebeen printed by the disqualified nozzle, per numeral 436. For example,in one embodiment, a print head has nozzles arranged both in rows andcolumns, such that if one nozzle is aberrant, a different, redundantnozzle can be used to deposit the droplet desired for a particular gridpoint. Optionally also, such issues can be taken into account and usedto adjust a scan path, for example, offsetting the print head in amanner such that the desired droplet(s) can be deposited using adifferent nozzle (with the print head adjusted in position so as topermit this). This is represented by the numeral 437 in FIG. 4B.Alternatively, an error can be generated (438) and used to promptsoftware to select a different halftone pattern (e.g., that relies on adifferent nozzle). Many such alternatives are possible. As representedby numerals 440 and 441, in one embodiment, each nozzle is calibrated inadvance using a droplet measurement device (440) that repeatedlymeasures droplet parameters (to develop a per-nozzle or per-drivewaveform distribution of measurements), with software then building astatistical model (441) for each nozzle with an understanding of nozzledroplet means for volume, velocity and trajectory, and with anunderstanding of expected per-nozzle variance for each of theseparameters. This data can be used to qualify/validate specific nozzles(and/or droplets), as mentioned, or to select nozzles or nozzlewaveforms that will be used to produce each individual droplet. Eachsuch measurement/error correction process can be factored into printplanning (431), including scan path planning, i.e., such that printerdata (or print control instructions) are generated and/or updated so asto optimize the print process, while ensuring desired layer properties.Finally, per numeral 445, final printer data (e.g., a final print imageor other printer control instructions) is then generated for sending tothe printer at fabrication time.

As noted, in order to assess the need for error correction, acalibration process can be performed specific to the ink, machine andprocess that will be used to form the desired layer of material. In oneembodiment, therefore, techniques introduced herein can be applied totest droplet and/or halftone parameters and to provide inputs thatultimately affect the halftone pattern or final print image. Forexample, such calibration can be used to gauge grayscale values (e.g.,in order to determine which grayscale values to apply to particulardesired thicknesses) or to calibrate halftone generation so thatgenerated halftone patterns reliably map assigned grayscale values tothe desired thicknesses. Other alternatives are also possible. Exemplarytechniques based on patterns are generally designated by numeral 451 inFIG. 4C, while exemplary techniques based on individual dropletmeasurement and nozzle qualification are explained in reference to FIG.4D.

As part of the calibration process, a halftone pattern (or associatedhalftoning parameters) can be assigned to thickness data (452) togenerate a print image 453 representing a layer. The layer can be partof a test run, for example, selected to provide uniform layer thicknessatop a flat substrate, but alternatively, can be data correlated inadvance with expected results. In one embodiment, the data can representa standard applied in a “live” print process or product run. As before,the print image is formed by translating desired layer thickness foreach of plural print cells into associated grayscale values (i.e., witha grayscale value for each print cell). Each per-print cell grayscalevalue is used to select a halftone pattern. In this embodiment also, thehalftone pattern is optionally selected to produce amacroscopically-continuous film (e.g., so as to produce a layerimpervious or resistant to penetration by water or oxygen). Asrepresented by alternate flow paths 455 and 457, the halftone printimage can be used either to control a printer in an actual depositionprocess or can be applied to a simulation process (i.e., by a softwareprogram) to simulate/estimate qualities of the finished layers, givenany other pertinent process parameters (e.g., dot gain for a particularink formulation, measured droplet volumes and so forth). For example,with a test deposition, a resultant device could be measured with astylus profilometer, optical interferometer or camera, with the resultsused to assess layer quality. See, e.g., the discussion of FIGS. 7A and7D below. Any results are then analyzed, per numeral 459, to assessuniformity and presence of defects, holes or voids. More generally, theresults are compared by an error process (461) with expected results(462) to determine deviation. For example, a fabricated or simulatedlayer may be thinner in some areas than in other areas which, if auniformly flat layer was expected, might represent a failure in thenozzle firing pattern. The error process 461 detects such deviations andcorrelates deviations with specific types of errors. If no deviation isdetected, and the layer has exactly the correct thickness, the processtentatively associates the selected grayscale values with a specificthickness and updates stored data or other settings, as appropriate, pernumerals 463 and 465. Note that this association can later beadjusted/updated as necessary, via another loop or pass of theconfiguration method 451. The method 451 can then be repeated (466) forother desired layer thicknesses and/or gradients, in order to fullydevelop a comprehensive mapping between different selectable grayscalevalues and desired thicknesses. Per numeral 467, if deviation betweenthe simulated or physical layer and the expected data is detected,associated process parameters are responsively adjusted. As reflected bynumerals 468-472, some of the parameters that can be adjusted includeselected grayscale values (e.g., the relation of grayscale values tothicknesses is changed if the test layer is too thick or thin), factorsinfluencing dot gain (e.g., ink viscosity, surface tension or otherfactors) or drop coverage (e.g., droplet shape, size, driver waveform,etc.), grid spacing or mapping, or any other desired parameters. Theprocess can incrementally adjust (e.g., increment or decrement) eachsetting, store updated adjustment data (473) as appropriate, andoptionally repeat the method 451 to test the new settings. Once anyadjusted settings are determined to be correct (i.e., when error process461 detects no error), the settings and any adjustment data are storedper reference numeral 465. Note that in some applications (notnecessarily all), scaling of grayscale values to desired thicknesseswill be linear, such that this calibration process can be performedusing only a small number (e.g., 2) of data points. Once this process iscomplete, a complete mapping should be available that links eachpermissible grayscale value to a specific layer thickness. At thispoint, the method ends. Note that the method 451 can be performedmultiple times, e.g., to obtain halftone patterns to be applied for eachof multiple specific machines or print heads, for use in general acrossplural machines or print heads, for each different types of ink or layermaterials, or to customize process to any variable affecting thedeposition process.

In some applications, it might be desired to deposit a layer of materialover underlying structures, such as electric pathways, transistors andother devices. This might be the case where the desired application issolar panel or OLED fabrication, as non-limiting examples, and where thematerial layer is to “blanket” these structures. For example, thetechniques discussed above can be applied to deposit one or more organicbarrier or encapsulation layers, e.g., as part of an encapsulation layerstack that includes alternating organic/inorganic barrier layer pairs.In such an instance, it might be desired to have such encapsulationresult in a relatively flat post deposition surface, notwithstandingvarying topography created by underlying structures. To this effect, themethod 451 can also be optionally performed for a given design, asrepresented by process block 475, to develop print cell-level (e.g.,grayscale value) correction data that will be used to adjust thethickness of the encapsulation layer on a print cell-by-print cell basisto adjust jetted ink to account for variation in the height ofunderlying structures. Such correction data is optionally used todevelop a correction image that can be used to adjust desired layerthickness for a particular design or, alternatively, to update/overwriteoriginal thickness data by modifying grayscale values pre-deposition orby performing a second deposition. As an alternative, in manyembodiments, a smoothing or barrier layer can also be deposited prior toencapsulation using conventional techniques, so as to effectivelyplanarize the substrate prior to receiving the layer of interest. Forexample, a deposition process can be used to “fill in” and effectivelyplanarize top surface layers of the substrate and, subsequently,encapsulation can be added using the printing process and related dataconversions discussed herein. In yet another variation, in one errorprocess, if it is determined that certain nozzle sets or grayscalevalues produce volumes that are off target, the original grayscalevalues can be adjusted at the level of the grayscale print image tocorrect for this error also. In another embodiment, corrections can beapplied at the bitmap (i.e., print image) level. These processes aregenerally represented in FIG. 4C via the application of asubstrate-level “map” or set of correction values, e.g., to planarizeany deviation in a surface of a deposited layer. Whatever themotivation, numeral 475 represents that a correction can be applied,either to instructions for depositing ink, or via an additional postdeposition process, to adjust (i.e., to normalize) data so as to obtainlayer homogeneity.

FIG. 4D provides a flow diagram 481 relating to droplet measurement andnozzle qualification. In one embodiment, droplet measurement isperformed within a printer using a droplet measurement device to obtainstatistical models (e.g., distribution and mean) for each nozzle and foreach waveform applied to any given nozzle, for each of droplet volume,velocity and trajectory. That is, as noted earlier, droplet volume andother droplet parameters can vary, not only-nozzle-to-nozzle, but overtime, with each droplet varying according to statistical parameters.Thus, in order to model droplets and account for statistical variation,repeated measurements are taken and used to develop an understanding ofa mean (μ) and standard deviation (σ) for each of these parameters foreach nozzle. For example, during a calibration operation (or maintenanceoperation), a number of measurements (e.g., 6, 12, 18, or 24measurements) can be taken of droplets from a given nozzle and used toobtain a reliable indicator of droplet expected volume, velocity andtrajectory. Such measurements can optionally be dynamically performed,e.g., every hour, day or on another intermittent or periodic process.Note that as referenced above, some embodiments can assign differentwaveforms for use in generating droplets of slightly differentparameters from each nozzle (see FIGS. 3A-3C, discussed above). Thus,for example, if there are three choices of waveforms for each of a dozennozzles, there are up to 36 waveform-nozzle combinations or pairings, or36 different sets of expected droplet characteristics that can beobtained from the given set of nozzles; in one embodiment, measurementsare taken for each parameter for each waveform-nozzle pairing,sufficient to develop robust statistical model for each pairing andsufficient to have a high-confidence, narrow distribution of dropletvalues. Note that, despite planning, it is conceptually possible that agiven nozzle or nozzle-waveform pairing may yield an exceptionally widedistribution, or a mean which is sufficiently aberrant that it should bespecially treated. Such treatment applied in one embodiment isrepresented conceptually by FIG. 4D.

More particularly, a general method is denoted using reference numeral481. Data stored by the droplet measurement device 483 is stored inmemory 484 for later use. During the application of method 481, thisdata can be recalled from memory and data for each nozzle ornozzle-waveform pairing can be extracted and individually processed(485). In one embodiment, a normal random distribution is built for eachvariable, described by a mean, standard deviation and number of dropletsmeasured (n), or using equivalent measures. Note that other distributionformats (e.g., Student's-T, Poisson, etc.), can be used. Measuredparameters are compared to one or more ranges (487) to determine whetherthe pertinent droplet can be used in practice. In one embodiment, atleast one range is applied to disqualify droplets from use (e.g., if thedroplet has a sufficiently large or small volume relative to desiredtarget, then that nozzle or nozzle-waveform pairing can be excluded fromshort-term use). To provide an example, if 10.00 pL droplets are desiredor expected, then a nozzle or nozzle-waveform linked to a droplet meanmore than, e.g., 1.5% away from this target (e.g., <9.85 pL or >10.15pL) can be excluded from use. Range, standard deviation, variance, oranother spread measure can also or instead be used. For example, if itis desired to have droplet statistical models with a narrow distribution(e.g., 3σ<±0.5% of mean), then droplets from a particular nozzle ornozzle-waveform pairing with measurements not meeting this criteria canbe excluded. It is also possible to use a sophisticated/complex set ofcriteria which considers multiple factors. For example, an aberrant meancombined with a very narrow distribution might be okay, e.g., if it isdesired to use droplets with 3σ volume within 10.00 pL±0.1 pL, then anozzle-waveform pairing producing a 9.96 pL mean with ±0.08 pL 3σ valuemight be excluded, but a nozzle-waveform pairing producing a 9.93 pLmean with ±0.03 pL 3σ value might be acceptable. Clearly there are manypossibilities according to any desired rejection/aberration criteria(489). Note that this same type of processing can be applied forper-droplet flight angle and velocity, i.e., it is expected that flightangle and velocity per nozzle-waveform pairing will exhibit statisticaldistribution and, depending on measurements and statistical modelsderived from the droplet measurement device, some droplets can beexcluded. For example, a droplet having a mean velocity or flighttrajectory that is outside of 5% of normal, or a variance in velocityoutside of a specific target, could hypothetically be excluded from use.Different ranges and/or evaluation criteria can be applied to eachdroplet parameter measured and provided by storage 484.

Depending on the rejection/aberration criteria 489, droplets (andnozzle-waveform combinations) can be processed and/or treated indifferent manners. For example, a particular droplet not meeting adesired norm can be rejected (491), as mentioned. Alternatively, it ispossible to selectively perform additional measurements (492) for thenext measurement iteration of the particular nozzle-waveform pairing; asan example, if a statistical distribution is too wide as a function ofmeasurement error, it is possible to take additional measurements forthe particular nozzle-waveform, so as to improve confidence of averagedvalues (e.g., variance and standard deviation are dependent on thenumber of measured data points). Per numeral 493, it is also possible toadjust a nozzle drive waveform, for example, to use a higher or lowervoltage level (e.g., to provide greater or lesser velocity or moreconsistent flight angle), or to reshape a waveform so as to produce anadjusted nozzle-waveform pairing that meets specified norms. Per numeral494, timing of the waveform can also be adjusted (e.g., to compensatefor aberrant mean velocity or droplet volume associated with aparticular nozzle-waveform pairing). As an example, as noted earlier, aslow droplet can be fired at an earlier time relative to other nozzles,and a fast droplet can be fired later in time to compensate for fasterflight time. Many such alternatives are possible. Per numeral 496, anyadjusted parameters (e.g., firing time, waveform voltage level or shape)can be stored for use during print scan planning. Optionally, ifdesired, the adjusted parameters can be applied to remeasure (e.g.,validate) one or more associated droplets. After each nozzle-waveformpairing (modified or otherwise) is qualified (passed or rejected), themethod then proceeds to the next nozzle-waveform pairing, per numeral497.

FIG. 5A shows a first example 509 of a halftone pattern and anassociated, hypothetical grid. In FIG. 5A, the grid is seen to have fivevertically-separated or “y” coordinates (represented for example by axis511) and five horizontally-separated or “x” coordinates (represented forexample by axis 513). Note that typically a grid is much larger, and afive-by-five array of grid intersections is depicted simply for purposesof illustration. Each intersection between a vertical axis and ahorizontal axis defines a grid point, such as point 515. Each point thushas a coordinate set associated with it, expressed as p(x,y,n) in FIG.5A. The value “n” in this example refers to the n^(th) pass of a printhead, i.e., grid points can optionally be repeated during a printingprocess or made respective to different print heads or print headpasses. Given this coordinate system, points seen on the top line of thegrid in this example have coordinates p(x,y,n), p(x+1,y,n), p(x+2,y,n),p(x+3,y,n) and p(x+4,y,n); each depicted point in this example is thus apossible droplet coordinate associated with one pass of a single printhead. Naturally, this coordinate system is exemplary only, and any typeof coordinate system can be used. In FIG. 5A, a solid dot at aparticular grid point (such as at point 515) indicates that, accordingto a selected or calculated halftone pattern, an ink jet droplet is tobe dispensed at that point, while a hollow circle at a grid point (suchas at point 517) indicates that no ink droplet is to be dispensed atthat point. For the halftone pattern represented by FIG. 5A, forexample, ink will be dispensed at point 515 but not at point 517. Asmentioned, in one embodiment, each grid point, such as point 515,corresponds to an individual print cell; in other embodiments, this neednot be the case. The depicted grid coordinates and “dot” system shouldnot be confused with ultimate extent of area coverage from ink on aprintable surface of the substrate. That is, ink as a fluid will spreadand cover a larger surface area than represented by the dots 515 and 517seen in FIG. 5A, a result which is referred to as “dot gain.” The largerthe dot gain, the greater the spreading of each ink droplet. In theexample presented by FIG. 5A, assuming consistent grid spacing, theminimum dot gain should at least be sufficient to allow the minimumhalftone droplet density (e.g., given ink viscosity, manufacturer gridspecification and other particulars) to produce a continuous film. Inpractice, where a continuous film is desired, the dot gain willtypically be much larger than the distance between closest grid points,e.g., sufficient to account for no ink printed at the substantialmajority of the print cells, and with error diffusion relied upon (givenink viscosity) to provide homogeneity in the finished layer. Forexample, in a hypothetical case where every grid point exactlycorresponds to a respective print cell, if every print cell wereassigned the same grayscale value (e.g., “50%”), then half of the printcells would receive printed ink and half would not, with error diffusion(and ink droplet spreading) resulting in a homogeneous layer thickness.

By comparing the halftone pattern 509 of FIG. 5A to a halftone pattern519 seen in FIG. 5B, one can observe relative effects of FM halftoning.In the case of these FIGS, the ejected droplets are all depicted to bethe same size, so for a thicker layer, a denser droplet pattern is used(e.g., more solid dots at grid intersections), and for a thinner layer,a less dense droplet pattern is used (e.g., fewer solid dots at gridintersections). FIG. 5A shows an approximately 50% density of dropletsthat will achieve this effect, whereas FIG. 5B shows that all gridcoordinates (such as at point 515) have a solid circle, indicating adroplet firing at the particular grid coordinate. The depiction in FIGS.5A and 5B might therefore correspond to respective grayscale values of127 and 255, respectively (in a system having 256 possible values), or50% and 100% (in a percentage based system). Again, other numberingschemes are also possible and it should be understood that thecorrespondence between layer thickness and droplet density may bedependent on dot gain and/or may be nonlinear; for example, where theminimum number of droplets for the depicted 25 gridpoints needed toobtain continuous coverage is “5,” the halftone pattern of FIG. 5A mightcorrespond to a grayscale value of 40% ((13−5)/20).

Note that the “grid” typically represents all possible firing positionsof a group of ink jet nozzles and that each grid point in the halftoneprint image uses exactly 1-bit, denoting whether or not a droplet is tobe ejected; thus, different “x” separations depending on embodiment willrepresent different nozzle firing times and/or firing from differentprint heads and/or different print head passes. A nozzle error (e.g.,failure to fire) will appear as a regular pattern and can be detectedthrough errors in a deposited layer. Reflecting back on the discussionearlier, related to error correction, if it is determined in practicethat a particular nozzle does not operate, the depicted grid might beprinted with errors that would be observed as thickness variation in thedeposited layer. To mitigate this error, the halftone pattern(s) (orgrayscale value(s)) could be adjusted so as to increase ejected inkvolume for adjacent grid positions, or otherwise change drop shape,frequency or firing time. Mitigation is seen in FIG. 5E for example,where it is noted that droplets 535 (from adjacent working nozzles) aredeliberately larger to account for missing droplets 533 that should havebeen printed by a defective nozzle. Alternatively, per FIG. 5F, if arelatively sparse droplet pattern is applied (e.g., per the example ofFIG. 5A) but a nozzle is misfiring and thus incapable of ejectingdroplets at position 537, the droplets can be moved into adjacent lines(539/541) printed by working nozzles to maintain local droplet density.Other examples are also possible. Corrections can optionally be appliedusing any of the mentioned techniques, e.g., increasing or decreasingdroplet size, moving droplets in a local area, adjusting electricalfiring pattern for a nozzle, adding print head passes, increasing sizeor shape of selected droplets, and so forth.

FIG. 5C provides a third example halftone pattern example, 521. Takentogether with pattern 509 seen in FIG. 5A, FIG. 5C provides an exampleof amplitude modulated (“AM”) halftoning, where apparent droplet size isvaried by providing a variable concentration (or cluster) of droplets,depending on grayscale value(s). For example, a concentration of dotscentered at point 525 represents the same ink volume as the pattern fromFIG. 5A, with individual droplets again fired on a binary decisionbasis, but with the relative concentration of droplets regionallyvaried. AM halftoning can therefore also optionally be used to varylayer thickness over an area of substrate. As with the examples before,thickness data for a desired layer can be converted to grayscale values,and the grayscale values can then be mapped to a halftone pattern; whereAM halftoning is used, larger grayscale values result in a generallycorresponding area of the substrate receiving larger apparent droplets.

FIG. 5D provides a grid depiction used to illustrate optional variationof halftone patterns to “stitch” together adjacent tiles of thesubstrate, to avoid Mura effect. In such an optional embodiment,halftone patterns for each of multiple “tiles” can be made dependent onpatterns selected for adjacent tiles to provide for seamless dropletdensities across tiles. For example, FIG. 5D shows a hypotheticaldroplet deposition pattern 541 where a first region 543 is seen tocorrespond to the pattern of FIG. 5A (approximately 50% halftoning) andwhere a second region 545 has a similar halftone pattern, also providing50% density. Generally speaking, this FIG. represents a situation wheredifferent regions of the substrate receive independently generatedhalftone patterns, and where it is desired to “stitch” adjacent patternstogether in a manner that is complementary, i.e., to avoid Mura. Forregion or “tile” 545, the halftone pattern is therefore seen to bevaried (e.g., inverted in this case) and selected such that seamlessblending between tiles 543 and 545 occurs. To provide an example, if thepattern from FIG. 5A was selected for both print regions or tiles (i.e.,543 and 545), then each of adjacent grid coordinate pairs p(x+4,y,n) andp(x+5,y,n), p(x+4,y+3,n) and p(x+5,y+3,n) and p(x+4,y+5,n), p(x+5,y+5,n)would be represented using black-filled circles, corresponding to alocal increase in droplet density. By selecting the halftone pattern fortile 545 in a manner dependent on the pattern selected for tile 543, anappropriate pattern can be selected that provides for seamlesstransitions in droplet pattern between tiles. There are also othertechniques for achieving variation, such as rotation of halftonepatterns (e.g., using the techniques discussed above in connection withFIGS. 3A-C), and so forth. Note that as depicted in FIG. 5D, both tilesuse a common grid, such as represented by a common horizontal axis 511;this facilitates seamless stitching so as to avoid existence of a defectin between tiles. Tiles (i.e., independent halftone pattern selectionfor different, abutting substrate regions) can be used in oneembodiment, but are, generally speaking, not required to implement thetechniques described herein.

The various halftone patterns introduced above for FIGS. 5A-5F areprovided as illustrative examples of halftone patterning only. Manyadditional patterns can be conceived for a given grayscale value (or inkvolume). Any particular halftone pattern (or multiple patterns forrespective tiles) can be adjusted to correct for errors and otherwisepromote uniformity in the fabricated layer.

FIG. 6A provides a table 601 that exemplifies a number of print cells,such as print cell 603. Note that each cell contains a “grayscale”value, such as the value “203” depicted within print cell 603. All printcells having a non-zero value represent the deposition area that is toreceive the layer material to be jetted, i.e., each numerical valuerepresents a layer thickness for a substrate region corresponding to thex-y position of the corresponding print cell, where thickness has beenconverted to a grayscale value. This value can be empirically mapped inadvance to the desired thicknesses (e.g., 1.0 micron thickness to a 10%or “25.5” grayscale value as a hypothetical example), with such mappingpossibly varying dependent on ink, printer, temperature, process andother parameters. Alternatively, as the end goal is that the assignedhalftone pattern should provide an ink volume that will correspond todesired thickness, variable mapping can be provided between the assignedgrayscale values and halftone pattern selection. Thus, in oneembodiment, the grayscale values assigned to various thicknesses arefixed (e.g., 10% of maximum value per micron of thickness, following thehypothetical just presented) but with a variable mapping between eachgrayscale value and halftone pattern selection. Other variations arealso possible.

Note that, as alluded to earlier, there exist alternate error correctiontechniques (i.e., besides adjustment of individual nozzle particulars).Thus, FIG. 6B shows a grayscale image 611 that is similar to FIG. 6A,but where the last row (i.e., represented by print cell 603) has had itsgrayscale values increased, i.e., by “5” in this hypothetical example.Assuming a left to right scanning motion relative to the orientation ofFIG. 6B, if it were determined (e.g., empirically or automatically) thatnozzles corresponding to this last row tended to produce low volumedrops, the grayscale data could be increased for the affected printcells such that, when printed, any aberrations in layer thickness arecorrected. Conversely, if a particular row of print cells featured highdrop volumes, it would be possible to artificially decrease grayscalevalues pertinent to affected print cells so as to planarize theresultant layer. Such a technique is especially useful where print cellsize corresponds to each point of the halftone/print grid. Note thatsuch adjustment need not be done by row or column or by scan path, i.e.,it is possible to apply error adjustment on the basis of a maprepresenting all or part of a printing substrate to adjust the grayscalevalues assigned to select print cells. As will be discussed below andelsewhere herein, such techniques can also be employed to vary edgebuild-up, i.e., to promote uniformity right up to a boundary or edge ofthe deposited layer.

FIG. 7A provides a graph, generally designated by numeral 701, showingthickness profiles of fabricated films obtained with a stylusprofilometer, useful in connection with the calibration process seen inFIG. 4C. Following the production of actual test layers of material, orsimulation of those layers, grayscale values corresponding to an inkvolume can be correlated with different steps in layer thickness. Forexample, a first curve 703, representing a 1.0 micron thick layer, isassociated with a grayscale value representing an 8% fill (or 8% ofmaximum print cell ink volume for a given pass or operation). Note thatthe film is continuous, i.e., there are no gaps in the center of thelayer represented by curve 703, which is seen to have substantiallyuniform thickness. For a subsequent fabrication process, if a layerthickness of 1.0 micron was assigned by received layout data for thedeposited layer, this quantity of 1.0 micron would be converted to agrayscale value for each print cell, as appropriate, and the grayscalevalue for print cells in a locality would then be applied to select ahalftone pattern that would distribute droplets to various halftone gridpoints associated with that locality in order to achieve a uniformdeposited layer (following droplet spreading). Similarly, a second curve705 is seen to represent a uniform 2.0 micron thick layer, correspondingto 16% fill. Based on such test or calibration data for the particularprocess, a halftone pattern correlated to 16% ink volume for aparticular substrate region might be generated to produce a 2.0 micronthick layer. Mappings between layer thickness values and/or grayscalevalues and/or halftone pattern selection can also be extrapolated usingthis process; as an example, if layout data called for a 1.5 micronthick encapsulation layer, grayscale values selected to correspond to apoint roughly between these two values (12%) could be applied (e.g.,halfway between 8% and 16%). Other illustrated curves 707, 709, 711 and713, respectively corresponding to 3.0, 4.0, 5.0 and 6.0 micron-thicklayers are associated with grayscale values of 24%, 32%, 40% and 50%,respectively. By specifically matching different grayscale values torespective layer thicknesses, and associating halftone patterning usedto deliver a corresponding amount of ink to a print cell, a designer cancustomize ink deposition to any desired thickness in a manner that willlead to predictable results; this provides a high degree of control overthickness of material deposited via fluidic ink.

In many applications, it is also desirable to provide a crisp, straightedge at border regions. For example, if a halftone pattern representinga low droplet density is selected for a border region, then it ispossible, given ink and deposition properties, that the deposited layerwill have a jagged, tapered or interrupted edge. To mitigate thispossibility, in one embodiment, software detects print cells that wouldproduce such an edge and adjusts halftoning (i.e., as a function ofgrayscale value gradient) to provide a crisp, straight edge that, ineffect, frames the deposited layer. For example, FIG. 7B provides a box725 representing a corner of a deposited layer, with grid points notshown. To produce a thin film, the halftone patterning can be maderelatively sparse in area 727. If used in border regions 729, 731, and733 this density may produce a jagged edge. Thus, the density ofdroplets in areas 729, 731 and 733 can be purposely increased to improveedge linearity. If box 725 represents a print cell along anintermediate, left edge of a deposited layer, it would suffice toincrease the density in area 729.

Note that in addition to adjusting gray scale values for border regions,it is also possible to adjust halftoning applied to such a region. Forexample, FIG. 7C shows an exemplary halftone pattern 741 that could beused where (as in the case of box 733 of FIG. 7B), the region representsthe corner of a deposited film; note that FIG. 7C is similar to FIGS.5A-5F in its use of a grid and solid fill circle to denote a dropletejection point. The particular halftone pattern represented in FIG. 7Crepresents the same ink volume as the pattern seen in FIG. 5A (i.e., 13of 25 possible droplets ejected). However, the pattern in FIG. 7Cfeatures relatively dense use of droplets along a top edge 743 of thesubstrate and a left edge 745 of the film, while interior region 747 isleft relatively sparse, i.e., to produce relatively crisp left and upperedges.

Note that the use of such framing or “fencing” techniques is notrequired for all embodiments, and it is within the capabilities of oneof ordinary skill in the art to determine the best strategy for aparticular application, ink and process technology.

FIG. 7D represents a graph 751 that illustrates how grayscale imageadjustment can be used to shape layer edges. More specifically, threecurves 753, 755 and 757 are presented in FIG. 7D, obtained using stylusprofilometer measurements of fabricated 6.0 micron encapsulation layers.The differences between these curves were produced by varying thegrayscale values applied to print cells that abut edges. Relative to abaseline represented by curve 753, curve 755 represents a process wherethe grayscale value (and associated ink volume for the print cell) isdecreased on approach to a boundary in the encapsulation layer (e.g.,before the encapsulation layer periphery). By contrast, curve 757represents a process where the grayscale value is increased for printcells abutting the same boundary; note that layer thickness actuallyincreases slightly immediately before the boundary, e.g., at x positionsof 2000μ and 17000μ. By adjusting the grayscale values for borderregions, a designer can adjust edge buildup at layer boundaries in adesired manner, including for purposes of providing a uniform layerthickness or surface, or smoothing or enhancing transitions. Note thatthe amount of the ink buildup adjacent to the layer edges will belargely dependent on ink properties, such as surface tension (and itsdependence on temperature). For example, some inks may naturally form alip, or so-called capillary ridge, (e.g., such as represented at point759 of curve 757); in such an event, the grayscale adjustment processjust described can be applied so as to remove this lip, e.g., to helptailor thickness of the ultimate layer by decreasing grayscale valuesfor print cells abutting a layer edge, such that the profile of thepermanent layer more closely matches curve 753.

Returning briefly to the discussion of edge enhancement (see thediscussion of FIG. 7C, above), it is also possible to employ multipleprocesses to tailor a layer's edge profile. FIG. 7E shows a portion of asubstrate 761 that is to have a central region 763 of uniform layerthickness, a border region 765 of “adjusted” droplet density (i.e.,selected so as to avoid edge buildup) and a set of fencing clusters 767selected to provide edge uniformity. Perhaps otherwise stated, centralregion 763 represents an area of substantially uniform ink volumedensity, border region 765 represents an area of adjusted ink density(e.g., reduced density) relative to the central region, and fencingclusters 767 represent a relatively dense ink density selected toprovide sharp, well-defined layer edges. In the presented example,halftoning might be performed based on uniform grayscale values in thecentral region (e.g., subject perhaps to nozzle error correction orunderlying substrate geography correction, depending on embodiment) andadjusted grayscale values in the border region (e.g., selected so as toavoid edge buildup “horns” 715, seen in FIG. 7A). Halftoning can bebased on the entire collection, or for example, the central and borderregion only (i.e., with fencing enforced following, and irrespective of,halftoning process). As should be appreciated by this example, manyvariations are possible which rely on grayscale and/or halftonevariation in order to tailor edge buildup and/or provide for desirededge characteristics.

Naturally, while this example has been discussed in terms of anencapsulation layer, these same principles can be applied to theformation of any desired layer. For example, it is expresslycontemplated that the described printing principles can be used tofabricate any of the HIL, HTL, EML, ETL or other layers of an OLEDdevice, for example, by way of illustration, with respective print wellsor on another patterned or unpatterned basis. Some examples will bediscussed further below.

FIGS. 8A-8E are used to narrate an exemplary fabrication process. Asimplied by FIG. 8A, it should be assumed for this narration that it isdesired to fabricate an array of flat panel devices. A common substrateis represented by numeral 801, and a set of dashed-line boxes, such asbox 803, represents geometry for each flat panel device. A fiducial,preferably with two-dimensional characteristics, is formed on thesubstrate and used to locate and align the various fabricationprocesses. Following eventual completion of these processes, each panel(803) will be separated from the common substrate using a cutting orsimilar process. Where the arrays of panels represent respective OLEDdisplays, the common substrate 801 will typically be glass, withstructures deposited atop the glass, followed by one or moreencapsulation layers. Light emission may occur through the glass or theencapsulation layers (depending on design). For some applications, othersubstrate materials can be used, for example, a flexible material,transparent or opaque. As noted, many other types of devices can bemanufactured according to the described techniques.

FIG. 8B is used to help illustrate fabrication of OLED panels.Specifically, FIG. 8B shows the substrate in a later stage of thefabrication process, after structures have been added to the substrate.The assembly is generally represented by numeral 811, and is seen tostill feature an array of panels on a common substrate. Featuresspecific to one panel will be designated using a numeral followed by arespective letter, for example, the letter “A” for a first panel, “B”for a second panel, and so forth. Each panel has a respective portion ofthe substrate, 812A/812B, for example, and an active region 813A/813Bthat contains light emitting layers. Generally speaking, the respectiveactive region will include electrodes and luminescent layers necessaryto provide pixilation and associated routing of electrical signals, suchas for control and power. This routing conveys power and controlinformation between respective terminals (e.g., 815A/B, 816A/B)associated with a terminal block 817A/817B and the active region for therespective panel. Typically, the encapsulation layer must provide aprotective “blanket” over the active region only (i.e., to sealelectroluminescent materials) while permitting unimpeded external accessto the terminal block 817A/B. Thus, a printing process must depositliquid ink in a manner that reliably and uniformly covers the activeregion (813A/813B) without gaps, holes or other defects, while at thesame time reliably and uniformly not covering the terminal block817A/817B. The active region is thus said to form a “target region” thatwill receive deposited ink to form the desired layer, while the terminalblock forms part of an “exposed region” that will not receive the ink.Note in FIG. 8B the use of numeral 818 to denote an xyz coordinatesystem and the use of numeral 819 to reference respective sets ofellipses to indicate presence of any number of panels replicated in xand y dimensions of the array.

FIG. 8C illustrates a cross-section of the assembly 811, taken alonglines C-C from FIG. 8B. In particular, this view shows the substrate812A of panel A, the active region 813A of panel A, and conductiveterminals (815A) of panel A used to effect electronic connection to theactive region. A small elliptical region 821 of the view is seenmagnified at the right side of the FIG. to illustrate layers in theactive region above the substrate 812A. These layers respectivelyinclude an anode layer 829, a hole injection layer (“HIL”) 831, a holetransport layer (“HTL”) 833, an emissive or light emitting layer (“EML”)835, an electron transport layer (“ETL”) 837 and a cathode layer 838.Additional layers, such as polarizers, barrier layers, primers and othermaterials can also be included. When the depicted stack is eventuallyoperated following manufacture, current flow removes electrons from theEML, and resupplies of those electrons from the cathode to cause theemission of light. The anode layer 829 typically comprises one or moretransparent electrodes common to several color components and/or pixelsto attract and remove electrons; for example, the anode can be formedfrom indium tin oxide (ITO). The HIL 831 is typically a transparent,high work function material that will form a barrier to unintendedleakage current. The HTL 833 is another transparent layer that passeselectrons from the EML to the anode, while leaving electrical “holes” inthe EML. Light generated by the OLED originates from recombination ofelectrons and holes in the EML material 835; typically, the EML consistsof separately-controlled, active materials for each of three primarycolors, red, green and blue, for each pixel of the display. In turn, theETL 837 supplies electrons to the EML from the cathode layer to eachactive element (e.g., each red, green or blue color component). Finally,the cathode layer 838 typically consists of patterned electrodes toprovide selective control to color component for each pixel. Lying atthe rear of the display, this layer is typically not transparent, andcan be made from any suitable electrode material.

As noted, layers in the active region can be degraded through exposureto oxygen and/or moisture. It is therefore desired to enhance OLED lifeby encapsulating these layers, both on faces or sides (822) of thoselayers opposite the substrate, as well as lateral edges, designated bynumeral 823. The purpose of encapsulation is to provide an oxygen and/ormoisture resistant barrier, as mentioned.

FIG. 8D shows an aggregate structure 839 where encapsulation 840 hasbeen added to the substrate. Note that the encapsulation 840 nowencloses faces 822 and lateral edges 823 relative to the substrate 812Aand that the encapsulation extends laterally to occupy a deposition arealarger than the underlying active layers; at a terminus of this area,the encapsulation forms a gradient or border region to help enclose/seallateral edges of the active region 813A. This is observed in detail atthe left side of FIG. 8D within a magnified elliptical region 841. Asseen in this expanded view, the encapsulation comprises a number of thinlayers, for example, alternating organic and inorganic layers, whichprovide a barrier against moisture and oxygen. The organic encapsulationlayers can be advantageously deposited using the techniques introducedabove, with the thickness of each individual layer regulated using thementioned techniques. Relative to a particular organic encapsulationlayer 842, a first region 843 overlies underlying structures, such asthe mentioned electrodes and the other OLED layers discussed above. Asecond region 845 operates as a buffer region, i.e., to maintain asubstantially uniform surface 846 that is planar with the first region843. Optionally, deposited thickness can be the same in both of regions843 and 845, but this need not be the case for all deposition processes.Irrespective of region, an ink jet printing process, using halftoning totranslate layer thickness, can be used to control thickness and promoteuniformity of the particular encapsulation layer 842. Finally, a third,gradient or border region 847 represents a transition to an exposed areaof the underlying substrate (e.g., to provide electrical terminals forthe active region). Numeral 849 indicates an associated taper in theencapsulation surface as it transitions to exposed substrate.

FIG. 8E is used to help illustrate the use of processing to adjustmaterial thickness at layer edges in the context of an OLED panel. Theseprocesses were generally introduced earlier in connection with FIGS.7B-7E. For example, in an encapsulation process such as the onediscussed, it can be desirable to ensure consistent layer thickness allthe way to a planned encapsulation periphery in order to provide forreliable edge sealing of any underlying sensitive material layers. Notethat the use of “fencing” as was seen in FIG. 7E is not separately seenin this FIG., though the same fencing process could be used here. InFIG. 8E, the substrate is once again observed in a plan view, that is,from the same perspective as seen in FIGS. 8A and 8B (though depictionof the electrical terminals is omitted). Note the use of a fiducial 851to align processes such that an organic encapsulation layer is correctlyprinted over underlying substrate. The target region (representing areawhere the encapsulation layer is to be deposited) is seen to compriseregions 843 and 845 from FIG. 8D. Rather than have undesired edgeeffects given spreading of deposited ink and the effect of surfaceenergy/tension of that ink, the grayscale image can be adjusted (i.e.,before printing) so as to change grayscale values for individual printcells along the layer's edge and, in so doing, change the edge profileat a layer periphery. For example, grayscale values within region 845can be increased as depicted in FIG. 8E so as to optionally increase inkvolume in areas approaching the boundary. Note in this regard that thetarget region can initially be associated with a particular thickness,for example, represented by hypothetical grayscale value “220” in thisexample. If it is determined empirically that due to ink spreading, atransition (for example, at the boundary between regions 845 and 847)provides insufficient coverage, the grayscale value in that area can beselectively increased to provide mitigation, for example, by increasingthe grayscale value (e.g., from “220” to “232” in FIG. 8E) for one ormore rows or columns of print cells representing the layer periphery. Asreferenced earlier, corrections can be stored as a correction image(e.g., as the corrections might, depending on application, vary as afunction of process, temperature, ink and other factors), or they canoptionally be incorporated into the layout data, grayscale image orother stored data. Note that where multiple boundary conditions arepresent, for example, intersection of two borders, it may be desired toprovide further adjustment, such as the depicted grayscale value of“240” for corner print cell 863. Clearly many possibilities exist. Byadjusting droplet density in these border regions, the techniquesintroduced above permit customized control over the layer edges in anymanner suitable to the particular deposition process at issue, forexample, to facilitate edge sealing of flat panel devices. Note that itis also possible for software to automatically provide for adjustedprint cell fill (i.e., to adjust grayscale values) according to aselected scaling factor any time the software detects print cells withina defined distance from a layer edge. Fencing can be added before orafter a grayscale image is sent for halftone generation, depending ondesired embodiment or effect.

FIG. 9 presents a method generally represented by numeral 901. In thisexample, it should be assumed that it is desired to deposit a layer aspart of an encapsulation process of a device such as a flat paneldisplay or a solar panel. The encapsulation is used to help protectinternal materials of the device from exposure to moisture or oxygen,thus prolonging expected lifetime of the device. This application is butone application for disclosed techniques, and nearly any type of layer(organic or inorganic), for nearly any type of device that is to receivea printed layer of material can benefit from the teachings herein.

It will be assumed for this discussion that the layer will be an organicmaterial deposited over a substrate, as part of a repeating stack ofalternating organic and inorganic materials layers; as many pairs ofsuch layers are built up, this stack will encapsulate sensitivematerials against a specific layer of the substrate. For example, in anOLED device, an electrode, one or more emissive layers, a secondelectrode and alternating organic/inorganic encapsulation layer pairscan be deposited over a layer of glass, with the encapsulation (oncefinished) sealing the emissive layers (including lateral edges of theemissive layers) against the glass layer. Typically, it is desired tominimize exposure of the assembly to contaminants during the fabricationprocess until the encapsulation has been completed. To this effect, in aprocess described below, while the various layers are added, thesubstrate is kept in one or more controlled environments until theencapsulation has been completed. The encapsulation can be formed usinga multi-chambered process where the substrate is subjected toalternating deposition processes to form the organic and inorganic layerpairs. In this example, it is assumed that the techniques introducedabove are applied to deposit an organic layer within the encapsulationstack and that this layer is typically deposited in liquid form and thenhardened or otherwise cured to form a permanent layer prior to additionof the next (inorganic) layer. An ink jet printing process can beadvantageously used to deposit this organic layer according to theprinciples introduced above.

Note that a “controlled atmosphere” or “controlled environment” as usedherein refers to something other than ambient air, i.e., at least one ofthe composition or the pressure of a deposition atmosphere is controlledso as to inhibit introduction of contaminates; an “uncontrolledenvironment” means normal air without means of excluding unwantedparticulates. In connection with the process depicted by FIG. 9, boththe atmosphere and pressure can be controlled, such that depositionoccurs in the presence of an inert material, such as nitrogen gas, at aspecified pressure, free from unwanted particulates. In one embodiment,a multi-tool deposition mechanism can be used to alternately depositorganic and inorganic layers of an encapsulation of sensitive materials,for example, using different processes. In another embodiment, amulti-chambered fabrication mechanism is used, such that some processing(e.g., active layer or inorganic encapsulation layer deposition) occursin one chamber while a printing process using the principles introducedherein is applied in a different chamber; as will be discussed below, amechanical handler can be used to automate transportation of thesubstrate from one chamber to the next without exposing the substrate toan uncontrolled environment. In still another embodiment, continuity ofthe controlled environment is interrupted, i.e., the other layers arefabricated elsewhere and the substrate is loaded into a depositionchamber, a controlled atmosphere is introduced, the substrate is cleanedor purified, and then the desired layer is added. Other alternatives arealso possible. These different embodiments are variously represented byFIG. 9. FIG. 9 expressly shows two optional process integrations,including integration (903) of fabrication of an inorganic encapsulationlayer (and/or one or more other layers, such as active layers) withdeposition of an organic encapsulation layer in a secured environment(e.g., not exposed to uncontrolled atmosphere) and/or integration (904)of the deposition of the organic encapsulation layer with a subsequentdrying, curing or other process, to solidify the organic encapsulationlayer and otherwise finish the layer as a permanent structure. For eachoptional integration process, the mentioned steps can be performed inone or more controlled environments that are uninterrupted by exposureto an uncontrolled environment (e.g., ambient air). For example, amulti-chamber fabrication device with means for controlling thedeposition environment can be used, as mentioned.

Irrespective of embodiment, the substrate is positioned for patterningand/or printing as appropriate. Accordingly, registration is firstperformed (905) using fiducials (or recognizable patterns) on thesubstrate. Typically, a fiducial will consist of one or more alignmentmarks that identify each region that is to be printed. As an example, asintroduced earlier (see, e.g., element 805 from FIG. 8A), several flatpanels can be fabricated together and cut from one die or commonsubstrate; in such a case, there might be a separate fiducial for eachpanel, positioned so that the printing mechanism and associated processcan be precisely aligned with any pre-patterned structures for eachpanel. Note, however, that fiducials can be used even where a singlepanel is to be fabricated. As will be further discussed below, thedeposition system can include an imaging system having a knownpositional relationship relative to the printing mechanism, with digitalimages of the substrate fed to a processor or CPU and analyzed usingimage analysis software to precisely identify the fiducials. In oneoptional variation, there are no special marks added to the substrate,i.e., the printing system recognizes its target by simply identifyingany existing structures (such as any previously-deposited particularelectrode or particular electrodes) and aligns to this pattern. Notealso that, advantageously, each fiducial represents a two dimensionalpattern, permitting correction of position and any substrate skew priorto deposition.

One or more layers are then added to the substrate, for example,consisting of one or more emissive layers, electrode layers, chargetransport layers, inorganic encapsulation layers, barrier layers and/orother layers or materials (906). As mentioned, deposition in oneembodiment is performed in a controlled environment (907), optionally inan inert atmosphere (909) such as nitrogen gas or a noble gas. Followingthis processing, an organic encapsulation layer is deposited as a liquidink, as represented by numeral 911. In contradistinction to otherpossible processes (e.g., used to add a mask layer), the ink in thisembodiment directly provides the material that will form the desiredlayer following cure, hardening, etc. Note also that the printingprocess is also advantageously performed in a controlled environment(907), such as in an inert atmosphere (909), and that the processes canbe repeated and alternated as denoted by the fact that connection arrowsare bidirectional; for example, a stack of inorganic and organicencapsulation layer pairs can be built up as introduced earlier.

FIG. 9 also shows various process options to the right of process box911. These options include the use of a multi-atmosphere process (913),the deposition of the organic encapsulation layer as a liquid ink (915),the deposition of the organic encapsulation layer atop a non-planarsubstrate (917), the use of a target deposition region of the substrate(that will receive the encapsulation layer) and an exposed region of thesubstrate (that will not be enclosed by the encapsulation layer) (919)and the generation of a border region (or gradient region) that willseal lateral edges of any underlying layers (e.g., from halftoningspecific to a border region or gradient filtering, 921), as discussedabove in connection with FIGS. 7A-7E.

Once each organic encapsulation layer has been deposited, as discussedabove, the layer is dried or otherwise cured (925) to render the layerpermanent. In one embodiment, the organic encapsulation layer isdeposited as a liquid monomer or polymer, and following deposition, anultraviolet light is applied to the deposited ink to cure the materialand harden it and form a layer of the desired thickness. In anotherpossible process, the substrate is heated to evaporate any solvent orcarrier for suspended materials, which then forms a permanent layerhaving the desired thickness. Other finishing processes are alsopossible.

Finally, once all encapsulation processes (including the desired numberof organic and inorganic layer pairs) have been completed, the entiresubstrate can be removed from the controlled environment, per numeral927.

While the described process can be used to deposit encapsulation forsensitive materials, as discussed above, the same process can also beused to deposit many different and other types of layers as well,including inorganic layers and layers for non-electronic devices.

As shown by the description above, halftoning processes canadvantageously be used to fabricate layers of controlled thickness usingprint cell-to-print cell and/or nozzle-to-nozzle control over inkdensities. More specifically, the described techniques are especiallyuseful where a liquid ink is used to deposit layer material of a desiredthickness. By selecting grayscale values and generating halftonepatterns that provide complete coverage (that is, to deposit a layer ofsufficient density to avoid defects or holes), a layer can beinexpensively and efficiently applied with localized control overthickness and uniformity, e.g., notwithstanding a liquid depositionmedium and any subsequent cure process. The disclosed techniques areparticularly useful for the deposition of homogenous layers such asblanket coatings, encapsulation layers, and other layers where featuresize is relatively large (e.g., tens of microns or more) compared to thewidths and feature definitions of any underlying electronic pathways. Asalso noted above, the disclosed techniques can be embodied in differentforms, for example, as software (instructions stored on non-transitorymachine-readable media), as a computer, printer or fabricationmechanism, as an information file (stored on non-transitorymachine-readable media) useful in instructing fabrication of such alayer, or in a product (e.g., a flat panel) made dependent on use of thedescribed techniques. Optionally also, error correction techniques canbe used to correct for droplet aberration from individual nozzles, toblend adjacent halftone patterns (e.g., for adjacent tiles), to correctgrayscale values to planarize the deposited layer, or for other effect.Several embodiments rely on error diffusion to ensure layer homogeneityand distribute droplet patterns in a manner that averages grayscalevalues for neighboring print cells. Again, many other applications willoccur to those skilled in the art.

The foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the disclosed embodiments. In some instances,the terminology and symbols may imply specific details that are notrequired to practice those embodiments. The terms “exemplary” and“embodiment” are used to express an example, not a preference orrequirement. Note that some elements described above can be described as“means for” performing a particular function. Generally, such “means”includes structure described above, including, where and as applicable,instructions stored on non-transitory machine-readable media (e.g.,software or executable instructions) that are written in a manner thatwill, when executed, cause at least one processor to perform aparticular function. Without limitation, specified functions can also beperformed by dedicated equipment, such as special purpose analog ordigital machines.

As indicated, various modifications and changes may be made to theembodiments presented herein without departing from the broader spiritand scope of the disclosure. For example, features or aspects of any ofthe embodiments may be applied, at least where practical, in combinationwith any other of the embodiments or in place of counterpart features oraspects thereof. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method of fabricating a thin film encapsulationlayer, the method comprising: for a first substrate, ejecting dropletsof liquid onto the first substrate with an ink jet printer, therebyforming a first liquid coat having a first volume per unit area of thesubstrate, and measuring a thickness of at least one of the first liquidcoat or a film formed by curing the first liquid coat; and for a secondsubstrate, ejecting droplets of the liquid onto the second substratewith the ink jet printer, thereby forming a second liquid coat having asecond volume per unit area of the substrate dependent on the firstvolume per unit area and a relationship of the measured thickness to atarget thickness, and curing the second liquid coat to form thethin-film encapsulation layer, wherein ejecting droplets onto the secondsubstrate comprises controlling at least one of an area density of thedroplets or a size of the droplets relative to at least one of dropletarea density or size used to produce the first volume per unit area. 2.The method of claim 1, wherein: the method further comprises receivingthe first substrate into a gas enclosure; ejecting the droplets onto thefirst substrate comprises printing the droplets onto the first substrateusing the ink jet printer within the gas enclosure; the method furthercomprises receiving the second substrate into a gas enclosure; andejecting the droplets onto the second substrate comprises printing thedroplets onto the second substrate using the ink jet printer within thegas enclosure.
 3. The method of claim 2, wherein the gas enclosureencloses at least one of nitrogen gas or a Noble gas, such that thedroplets of the liquid deposited onto the first substrate and thedroplets of liquid deposited onto the second substrate are eachdeposited within an atmosphere comprising the at least one, and whereincuring the second liquid coat is performed within a controlledatmosphere, the second substrate not being exposed to an un-controlledatmosphere in between ejecting the droplets to form the second liquidcoat and said curing.
 4. The method of claim 3, wherein ejecting thedroplets onto the second substrate using the inkjet printer is performedfor each substrate in a series of substrates, and wherein for eachrespective substrate in the series: ejecting the droplets is performedaccording to a common printhead scan pattern and a common nozzle firingpattern; the respective substrate comprises an active region, an exposedregion and a buffer region between the active region and the exposedregion, the active region to receive the thin film encapsulation layerat a uniform thickness corresponding to the desired thickness, theexposed region not to receive the thin film encapsulation layer, thebuffer region to provide a transition between the active region and theexposed region; and the buffer region is to receive the thin filmencapsulation layer according to a third volume of the liquid depositedper unit area, relative to the active region.
 5. The method of claim 4,wherein: the third volume per unit area is selected according to acalibration process performed on a test substrate, the calibrationprocess to measure deviation between a lip of a deposited layer and theuniform thickness; and the third volume per unit area is selected so asto reduce the deviation.
 6. The method of claim 5, wherein the testsubstrate is the first substrate.
 7. The method of claim 6, wherein theliquid comprises a monomer and wherein curing the second liquid coatcomprises exposing the second liquid coat to ultraviolet radiation toconvert the monomer to a polymer.
 8. The method of claim 1, embodied asa method of manufacturing an electronic device, the electronic devicehaving light emitting elements, wherein the second substrate is receivedin a manner having the light emitting elements, and wherein the secondliquid coat and the thin film encapsulation layer are to cover the lightemitting elements.
 9. A method of fabricating thin film encapsulationlayers, the method comprising: in a calibration process, ejectingdroplets of liquid onto a first substrate with an ink jet printer,thereby forming a first liquid coat having a first volume per unit areaof the substrate, and measuring a thickness of at least one of the firstliquid coat or a film formed by curing the first liquid coat; and in aproduction process, for each respective substrate in a series of secondsubstrates, receiving the respective substrate, ejecting droplets of theliquid onto the respective substrate with the ink jet printer, therebyforming a second liquid coat having a second volume per unit area of thesubstrate dependent on the first volume per unit area and a relationshipof the measured thickness to a target thickness, and curing the secondliquid coat to form one of the thin film encapsulation layers on therespective substrate, wherein ejecting droplets onto the secondsubstrate comprises controlling at least one of an area density of thedroplets or a size of the droplets relative to at least one of dropletarea density or size used to produce the first volume per unit area. 10.The method of claim 9, wherein the liquid comprises a monomer andwherein curing the second liquid coat comprises exposing the secondliquid coat to ultraviolet radiation to convert the monomer to apolymer.
 11. The method of claim 9, embodied as a method of forming thethin film encapsulation layer in an electronic device having lightemitting elements, and wherein: the method further comprises receivingthe first substrate into a gas enclosure, the first substrate having thelight emitting elements formed on the first substrate, the first liquidcoat to cover the light emitting elements; ejecting the droplets ontothe first substrate with the ink jet printer comprises printing withinthe gas enclosure; receiving each respective substrate in the seriesfurther comprises receiving the respective substrate into the gasenclosure, the respective substrate also having the light emittingelements formed on the respective substrate, the second liquid coat tocover the light emitting elements; and ejecting the droplets onto therespective substrate with the ink jet printer also comprises printingwithin the gas enclosure.
 12. The method of claim 11, wherein the gasenclosure encloses at least one of nitrogen gas or a Noble gas, suchthat the droplets of the liquid are deposited onto the first substrateand each respective substrate within an atmosphere comprising the atleast one, and wherein curing the second liquid coat is performed foreach respective substrate in the series within a controlled atmosphere,each respective substrate in the series not being exposed to anuncontrolled atmosphere in between ejecting the droplets to form thesecond liquid coat and said curing on the respective substrate.
 13. Themethod of claim 9, wherein each respective substrate in the seriescomprises an active region, an exposed region and a buffer regionbetween the active region and the exposed region, the active region toreceive the thin film encapsulation layer at a substantially uniformthickness corresponding to the target thickness, the exposed region notto receive the thin film encapsulation layer, the buffer region toprovide providing a transition between the active region and the exposedregion; and for each respective substrate in the series, the bufferregion is to receive the thin film encapsulation layer according to athird volume of the liquid deposited per unit area, relative to theactive region.
 14. The method of claim 13, wherein: the third volume perunit area is selected according to a calibration process performed on atest substrate, the calibration process to measure deviation between alip of a deposited layer and the uniform thickness; and the third volumeper unit area is selected so as to reduce the deviation.
 15. The methodof claim 14, wherein the test substrate is also one of the respectivesubstrates in the series.
 16. A method of fabricating a thin filmencapsulation layer of electronic devices, each of the electronicdevices having light emitting elements, the method comprising: in acalibration process, ejecting droplets of liquid onto a first substratewith an ink jet printer, thereby forming a first liquid coat having afirst volume per unit area of the substrate, and measuring a thicknessof at least one of the first liquid coat or a film formed by curing thefirst liquid coat; and in a production process, for each respectivesubstrate in a series of second substrates, each of the secondsubstrates having the light emitting elements, receiving the respectivesubstrate, ejecting droplets of the liquid onto the respective substratewith the ink jet printer, thereby forming a second liquid coat so as tocover the light emitting elements of the respective substrate, thesecond liquid coat having a second volume per unit area of the substratedependent on the first volume per unit area and a relationship of themeasured thickness to a target thickness, and curing the second liquidcoat to form one of the thin film encapsulation layers on the respectivesubstrate, wherein the liquid comprises an organic material, whereinejecting droplets onto the second substrate comprises controlling atleast one of an area density of the droplets or a size of the dropletsrelative to at least one of droplet area density or size used to producethe first volume per unit area, and wherein curing the second liquidcoat comprises polymerizing the organic material.
 17. The method ofclaim 16, wherein: the method further comprises receiving the firstsubstrate into a gas enclosure; ejecting the droplets onto the firstsubstrate with the ink jet printer comprises printing within the gasenclosure; receiving each respective substrate in the series furthercomprises receiving the respective substrate into the gas enclosure;ejecting the droplets onto each respective substrate in the series withthe ink jet printer also comprises printing within the gas enclosure;and curing the second liquid coat is performed for each respectivesubstrate in the series within a controlled atmosphere, each respectivesubstrate in the series not being exposed to an uncontrolled atmospherein between ejecting the droplets to form the second liquid coat and saidcuring on the respective substrate.
 18. The method of claim 17, whereinthe gas enclosure encloses at least one of nitrogen gas or a Noble gas,such that the droplets of the liquid are deposited onto the firstsubstrate and each respective substrate within an atmosphere comprisingthe at least one, and wherein curing the second liquid coat is performedfor each respective substrate in the series within a controlledatmosphere, each respective substrate in the series not being exposed toan uncontrolled atmosphere in between ejecting of the droplets to formthe second liquid coat and said curing on the respective substrate. 19.The method of claim 18, wherein each respective substrate in the seriescomprises an active region, an exposed region and a buffer regionbetween the active region and the exposed region, the active region toreceive the thin film encapsulation layer at a substantially uniformthickness corresponding to the target thickness, the exposed region notto receive the thin film encapsulation layer, the buffer region toprovide providing a transition between the active region and the exposedregion; and for each respective substrate in the series, the bufferregion is to receive the thin film encapsulation layer according to athird volume of the liquid deposited per unit area, relative to theactive region.
 20. The method of claim 16, wherein each of theelectronic devices comprises a pixelated organic light emitting diode(OLED) display device.